Let the stress begin! :(

A friend of mine asked me to take a look at her laptop due to recent overheating issues. She said that whenever it was running a movie or mp3s or a game, it would restart itself. She had managed to figure out that if she boosted it up on a cookie rack or something of the sort, it would cool better and not have the problem. However, she wanted me to see if I could fix it altogether...

This was the first laptop I've attempted to fix. First I downloaded some diagnostic utilities to see what her temps and fan speeds were. Everything seemed to be pretty normal to me, so I just blew everything out with a can of compressed air. After that, I decided to open it up and apply some Artic Silver 5 to the CPU/heatsink.

It was pretty simple to open it up, but in my lack of laptop experience, I forgot to take out the battery. As I was putting the CPU/Heatsink back in, the metal of the Heatsink touched the mainboard, and a small spark jumped between them! :(

Now the computer won't power up for more than a few seconds... When it is plugged into the wall, the front lights will flash on real fast, then flash off, and it doesnt show it as charging. When I turn it on, only the fan will start.. then it shuts itself off.

Do you think it is a bad mainboard? Or could it be the CPU?

Sounds like you shorted the mainboard. Unless you have the proper electronic test equipment and are very skilled at soldering, you are probably looking at replacing the board.