Chynx:
Nice thread!
OP, I think providing us with a link to your original source would help; as "link prompts" within your article are unavailable.

azubyky:
http://www.carparts.com/carrepair/nostart.htm

azubyky:

With today's computer controlled cars, the possibility of a vehicle not starting when you turn the key is less likely then ever before.  But it does happen, and when it does, it would help if you knew some basic tests and procedures that could allow you to determine the cause and often fix the problem yourself instead of relying on your local repair shop to bail you out.

The first step is to narrow down the cause of the no-start.

Let's go over the process of starting the car, so you have a better understanding of what is going on when you turn the key: 

Here is what happens on a properly running car:

You sit behind the wheel and insert the ignition key into the switch.
You then turn the key to the spring loaded start position.  When you do that, the ignition switch engages the starter by connecting the battery to the electric starter motor which, in turn cranks the engine over.  This can be easily heard and is referred to as cranking the engine over.
The next thing you will hear is the engine running, which is your signal to release the key.
At that point, the engine is running and you are ready to place the transmission selector in Drive and be on your way.
Please note: This article outlines basic problems, but it is not meant to be a do-it-yourself repair guide for resolving all possible no-start scenarios.  If  your mechanical experience is limited, this  information may be helpful as preparation for dealing with a repair shop.

A number of things can go wrong during the starting process.  The following should help you distinguish exactly where the problem is occurring in order to determine what needs to be done to resolve the situation and get on your way.

Key will not turn: 
This can happen for a couple of reasons:  The most obvious is that you are using a key not meant for that car or you have a worn out key.  If you have a spare, try that one. A very common problem can occur when you park with the wheels turned all the way to one side and remove the key.  When you try to turn the key to start, there is too much pressure on the steering lock to allow the key to turn.  To correct this, force the steering wheel, first in one direction, then the other, while trying to turn the key.  That should relieve the pressure and allow the key to turn.

Engine does not crank: 
When you turn the key to start, you may hear a single click or nothing at all, or you may hear a rapid series of clicks, like a woodpecker, or you may hear the cranking sound, but it goes very slowly.  The most common cause for any of these is either a weak or dead battery, or a dirty or corroded connection to the battery.  Before you go any further, turn your interior light on, then try to start the car.  If the light is dim or goes dim when you turn the key to start, then Click here to find out what to do when you have a dead battery.

If the interior light is bright when you turn it on and doesn't change when you turn the key to start, the battery is probably ok.  This condition can be caused by the following: (this list is sorted from most likely to least likely)

You do not have the transmission selector in park or neutral on an automatic transmission vehicle or there is a problem with the neutral safety switch.  Try starting again with the transmission selector in Neutral.
You are not depressing the clutch pedal all the way down on a standard transmission vehicle or there is a problem with the clutch pedal switch.
There is a problem with the ignition switch or connecting wiring.
There is a problem with the starter motor or starter solenoid.
Engine cranks normally, but it does not fire: 
You turn the key to start and hear the starter motor crank the engine, but when you release the key, the cranking stops and there is silence.  This means that the battery and starting motor are working properly, but the engine is not firing.  If you continue cranking the engine over in this way, the battery will eventually run down and will need to be recharged, but the battery and starter are not the cause of your problem.

There are a number of causes for this type of no-start condition, the most common being that you are simply out of gas.  Assuming that you have fuel in the tank, you will need to go through a series of tests to determine what is causing the problem.  The testing procedure requires that you use specialized equipment in order to determine the problem area.  There are three main tests in order to get you pointed in the right direction.  You will need to test for Spark, Fuel and Compression, in that order.  As soon as you see a problem in one of those areas, that is where you will need to concentrate your efforts.

Spark:
An easy way to test for spark is with an inexpensive spark tester.  This is a device that is readily available at most auto supply stores.  You use it by simply holding it next to a spark plug wire.  If you see the neon lamp flashing while someone cranks the engine, then you have spark and should move on to checking for fuel.  If there is no spark, or a very weak spark, you will have to do a series of methodical tests that vary depending on the type of vehicle.  You will need a repair manual for your car in order to get the correct diagnostic procedures.  A good source for on-line repair information at a reasonable price is Alldata-DIY.

Fuel:
First step here is to listen for the fuel pump running inside the gas tank.  When you turn the key to run, you should easily hear the pump come on, run for a few seconds to build fuel pressure, then turn off.  If you do not hear it, it could mean that the fuel pump or circuitry is bad.  (Fuel pump failure is a common problem on modern cars.)

Fuel injected cars are very sensitive to proper fuel pressure.  If the pressure is off, even by a few pounds, it will cause noticeable performance problems, or a no-start condition. To check for proper fuel pressure, you will need a fuel pressure gauge that is suitable for your type of system.  A fuel injected engine (found on just about every vehicle less than 20 years old) produces very high fuel pressures and requires a fuel pressure gauge that reads up to 100 pounds per square inch.  This type of gauge has a threaded connector that must match the pressure tap on your fuel rail.  Since you are working with a highly combustible fluid which can be quite dangerous if you do not know what you are doing, you should leave this step to a pro.

Compression:
If you know that you have spark and fuel, the next step is to check for compression.  For this, you will need a mechanic's grade compression tester that will screw into a spark plug hole.  You will need to remove the spark plugs and use the compression tester to test the compression on each cylinder.  If the compression is very low on all cylinders, that is a sure sign that the timing belt (or timing chain depending on the engine) has failed and will have to be replaced.

Engine runs, but car will not move when put in gear:
If the engine is running, but the car won't move when you put the transmission selector in gear, follow these steps:

Automatic Transmission: If you place the selector in Drive or Reverse, but the engine just races when you step on the gas and the car does not move or moves very slowly, it means that there is a problem with the transmission or driveline.  First thing to do is check the fluid level in the transmission.  In most cars, you check the transmission fluid level with the engine running in Park.  If the fluid level is very low, in short, you see no fluid on the dipstick, shut off the engine to avoid further damage to the transmission and call for a tow to a repair shop.  In some cases, a leak can be repaired fairly easily without a large expense (assuming the transmission wasn't damaged by running with low fluid levels).  If the fluid is full, there is a slight chance that the gearshift may have come disconnected, which means that you lucked out.  Otherwise, you are most likely facing an expensive transmission rebuild.

Standard Shift Transmission: If you put the transmission in gear, but when you release the clutch, the car does not move or moves very slowly even though the engine is racing, it is probably time to replace the clutch.  On some cars, you may be able to get by with a clutch adjustment, but if it has been slipping for a while, chances are that the friction surface of the clutch is burnt and will need to be replaced.

Dead Battery
One of the most common no-start conditions is caused by a dead battery.  This does not automatically mean that the battery is no good, it only means that the battery has lost its charge for one reason or another.
The reason for the battery in a car is to provide temporary power to start the car or to run some accessories (like lights or radio) when the car is turned off.  Once the car is running, the charging system (which consists of the alternator and voltage regulator along with the interconnecting wiring) will recharge the battery and provide all necessary electrical power to the vehicle.  The battery then only serves as a backup if the vehicle requires more electrical current than the charging system can provide.  This can happen when there is a high demand for electrical power, for instance on a cold, rainy night when you are in a traffic jam.  In this case, your lights and wipers are on, the heater fan is blowing on high, the brake lights are being activated and the alternator is not spinning fast enough to keep the power coming.  You may notice the lights dimming slightly, then brighten as you step on the gas.  In these cases, a battery in good condition is more than capable of taking up the slack to keep everything going.

There are a number of reasons for a battery to become discharged so that it no longer has the power to start the engine. 

The more common reasons for a dead battery are:

Forgetting the headlights turned on after you park the car.
Forgetting a reading light or courtesy light turned on. This is easy to do since most cars have a feature that delays turning off the interior lights after you leave the car, so that you don't notice that you left a light turned on.
A corroded or loose connection between the battery and the cables attached to it.
A defective interior or trunk lamp switch that leaves the bulb lit.
A defective charging system that does not replenish the battery's charge.
An old battery that has lost its ability to maintain a full charge.  Batteries have a life expectancy of 3 to 5 years, after which they should be replaced preventatively even if they are working well.  Batteries have to work much harder during winter months when it is cold out.  Sub freezing temperatures are when batteries usually begin to show signs that they are failing.
First, some important safety information:
The automotive battery requires special handling. The electrolyte inside thebattery is a mixture of sulfuric acid and water. Sulfuric acid is very corrosive; if itgets on your skin it should be flushed with water immediately; if it gets in your eyes, you should immediately flush them thoroughly with water and see a doctor right away.  In this situation, time is critical.  If you work with batteries often, you should have a mild solution of baking soda and water on hand and flush with that.  The baking soda will neutralize the acid and minimize the damage.  Remember: it is more important to flush immediately.  Do not take the time to make up a solution first.

Sulfuric acid will eat through clothing, so it isadvisable to wear old clothing when handling batteries. It is also advisable to weargoggles and gloves while servicing the battery. When charging, the battery will emithydrogen gas; it is therefore extremely important to keep flames and sparks away from thebattery.

Because batteries emit hydrogen gas while charging, the battery case cannot becompletely sealed. Years ago there was a vent cap for each cell and we had to replenishthe cells with distilled water when the electrolyte evaporated. Today's batteries (maintenance free) have smallvents on the side of the battery; the gases emitted have to go through baffles to escape.During this process the liquid condenses and drops back to the bottom of the battery.There's no need to replenish or add water to this type of  battery.

A car battery has two terminals either on top or on one site of the battery.  On top terminal batteries, one post is slightly larger than the other post.  The large terminal is the positive terminal and is marked with a prominent plus sign (+).  The smaller terminal is the negative terminal and is marked with a minus sign (-).  On a side terminal battery, the cables are screwed to the terminals.  They are also clearly marked with a + and - and are also color coded, Red for positive and Black for negative. 

The negative terminal is directly connected to the metal body of the car as well as the metal engine block.  This is also called the Ground.  The positive terminal is insulated and goes to all the components that require power.  The positive terminal must never come into contact with the body or you will cause a dangerous short circuit.

What to do when your battery is dead:
The first thing you can do is check the battery connections.  Find a pair of old gloves before you touch anything around the battery.  Touching battery terminals with your hand will not give you a shock since we are dealing with only 12 to 14 volts and it would take more than that before you would feel it.

If however, you touch the battery terminal with anything metal and allow the metal to come into contact with any metal on the car, you will get a severe spark that could cause injury and possibly ignite the hydrogen gas causing an explosion. So if you plan to do this yourself, you should feel confident in your abilities and follow all the safety precautions, otherwise seek the help of a professional automotive technician.

If you still plan to do this yourself, here are some procedures to follow: 

Once you are protected, grab each terminal and feel if the connection is loose on the battery.  Only use a small amount of pressure so you do not damage the battery post.  If you notice that one of the terminals is loose, just by moving it, you may be able to establish a good enough connection to start the car.

If it still won't start, you will need to either get a jump start or have the battery recharged using an external battery charger.

Getting a jump start:
There are a couple of ways to boost, or jump start a car with a dead battery.  You can get a Battery Booster Box, which is readily available in stores that sell automotive parts and accessories.  This is a device with a rechargeable battery in it that has two large clamps that are used to connect to the dead battery.  These booster boxes are recharged by plugging them into a regular wall outlet to keep them ready for use at a moment's notice.  Many of them also have an air compressor that can be used to inflate your tires, and a search light to provide emergency light on the side of the road.

The other way is to use another car and connect its good battery to the dead battery using Jumper Cables.  It is important to use good quality cables when trying to boost a car with a dead battery.  Using thin, cheap cables may not allow sufficient amperage through.  Furthermore, they can get very hot and fail, possibly causing serious burns or even fire.

When shopping for booster cables, look for heavy cable with insulated wire that is at least 6 gauge, with 4 gauge being better. (the lower the cable gauge, the thicker the wire).  Make sure that the wire goes all the way through the clamp and is connected directly to the jaw.  If the wire is connected only to the clamp grip, do not buy it.  Good jumper cables will cost more than $20 with professional quality cables costing $30 or more.  There are plenty of cables that cost as little as $5 to $10.  Stay away from those.

Booster cables have one black clamp on each end of one of the wires and a colored clamp, usually red or yellow, on each end of the other cable.  When connecting the cable clamps to a battery, it is imperative that you always clamp the positive clamp (Red) to the positive terminal (+) and the negative clamp (Black) to the negative terminal (-)

Batteries on newer cars are not always easily accessible, but when this is the case, they will have a battery tap somewhere in the engine compartment.  The positive side will usually be clearly marked under a red plastic protective cover.  The negative side may or may not be there, but you can always connect to the engine block or metal brackets that are directly attached to the engine.

Using another car for the jump start:

Important:  Check the owner's manual for both cars.  On some vehicles, the manufacturer does not recommend jump starting under any circumstances.  Other vehicles have specific steps that must be taken before jump starting, such as removing a certain fuse before proceeding.  Failure to follow these manufacturer's instructions can cause expensive damage to the vehicle electronics.  If the jump start procedure in either owner's manual is different from the instructions listed below, you should follow the instructions in the owner's manual instead.
When using another car with a good battery, follow these steps:

Get the front of the car as close as you can to the front of the disabled car, making sure that the two cars do not touch. 
Shut both cars off and open the hoods.
Wear suitable eye protection.
Connect the positive (+) cable (Red) clamps to the positive battery terminal on each car.
Make absolutely sure that you are connected to the positive terminals on both batteries with the same side of the cable (the connectors on each end of the cable are the same color (usually Red or Yellow)
Next, connect the negative (Black) clamp to the negative terminal on the good battery.  There should be no sparks)
This is important.  You will NOT be connecting the remaining clamp to the battery on the disabled car.
Find a place on the dead car to connect the other negative clamp away from the battery, either on the engine block or a metal bracket that is directly attached to the engine.  You most likely will see some small sparking.  If you get a big spark, either there is something not connected properly, or the battery is shorted out, in which case you should not attempt a jump start until you replace the bad battery.
Once you have the cables connected, you can try to start the disabled car.  If the only thing that was wrong was a discharged battery, the car should start up quickly.
If the car is still hard to start, first disconnect the negative cable from the bad car, then check to make sure that there is a good solid connection at each of the remaining cable clamps, then reconnect the negative clamp on the disabled car's engine block and try again.
If the cables begin to get hot, discontinue the boost immediately: the cables are not heavy duty enough to do the job.
Once the disabled car is running, first remove the negative cable from the engine block of the problem car, then remove the negative cable from the other car.
Finally, remove the positive clamps from both cars and close the hoods.
It is a good idea to keep the problem car running until you are able to have the battery recharged, either by driving on the highway or with a battery charger.
If you suspect that the battery did not discharge by something obvious, like forgetting the lights on, have the battery and charging system tested by someone with the proper equipment to do this, preferably a pro.