After checking the boot sequence, ensure that you don't have a floppy in any of the drives.
If it still doesn't boot, press your reset/power button, (as soon as something shows up/flashes on your screen, press F8 until until you arrive at a dailogue box suggesting various types of boot modes.
Select the boot to safemode (with network if the system has an internet connect) checkout the link below for what I'm talking about.
(If it boots up to this level, then there's hope for your system)
You can now try you recovery console to seen if you can take your system back to an earlier date when the system used to work properly.
If it doesn't boot to this level then I'll recommend a simple software you'll need to burn unto a CD (hope your system has a CD/DVD drive). (Pray that your hard disk isn't dead sha)
The burnt software boots you system to a level where you can recover virtually everything from you system, fix what it was you were doing before it went "kolo-mental" or outrightly reformat or partition the system. If you do eventually feel the need to reformat, ensure you have a Windows OS to reinstall all after.
I'll get you the name of the software later. Its free to download, less than 4 MB but it need to be burnt to CD. Load it in the CD drive before booting.