AC power adapter turns off when plugged into the laptop, under this circumstance the laptop is working fine. The LED indicator of the AC power adapter turns on when connected to power supply, showing that there is voltage supply to it, but as soon as the AC power adapter is plugged into the laptop, the LED indicator turns off which means that there is no way the laptop battery can be charged.

When you can not charge your battery or power your laptop using the power adapter, then it means that you can not use the laptop all. So many thoughts run through your mind on what could have caused the problem, you can not come up with any tangible solution. Possibly there is a short circuit somewhere causing the problem, troubleshooting the problem will help us solve this riddle.

Possible Faults

1.Faulty AC power adapter
2.Power setting
3.Motherboard failure

Solutions

1.Try using another AC power adapter to power the laptop, if it works (powers the laptop and charges the battery perfectly well) then the former adapter is faulty and is probably responsible for the short circuiting but if the problem still continues, then the fault is not from the power adapter, with this now the power adapter has been taken out of the equation, lets move to the next level of troubleshooting.

2.Check the power setting, It could be set to turn off when power cord plugged in. To check the setting right click the desktop anywhere that it's blank and choose properties from the menu that comes up. In the window, click the Screen Saver tab. Near the bottom, click the Power button. Look to see what it is set to do when plugged into AC power.

3.If you have tried the above steps and the laptop is still having the same problem, then it means that the motherboard is bad.You have the option of replacing the motherboard in order to rectify the problem or you can decide to continue using the laptop with the fault. This means that you can only charge the laptop only when it is turned off and you can only use the laptop when it is running on batteries.

Source: http://www.learnlaptoprepair..com/2013/07/how-to-repair-laptop-in-which-ac-power.html