|Be sure you are trained before you attempt this. If you are unsure then stop.|
What is the voltage on the main battery?
What is the voltage on the power adapter on computer side.
"friend suggested it might be the motherboard" This is a wild guess. Not worth comment. While it may turn out to be, you need to test.
Almost all modern laptops have a very complex scheme to shut down parts of the computer to save energy. The basic starting place is the power supply area of the laptop. It may or may not be on the motherboard. It may be a daughter board next to or attached to the main board.
Saying all that, my guess is, unless it is the power adapter or bad main battery or defective dc jack you are unlikely to be able to repair it cost effectively. Guessing with $300 boards is a very expensive way to learn.
"Best Practices", Event viewer, host file, perfmon, antivirus, anti-spyware, Live CD's, backups, are in my top 10