I went to hook my girlfriend's PC up for her, and when I went to turn it on...nothing happened.

I screwed around with the cords, tried switching them with new ones, tried a different socket, but no luck.

The keyboard somehow came unplugged without me knowing, and it suddenly worked. It turned on.

I went to plug the keyboard back in, and it shut off. For a few minutes, it would only turn on if the keyboard was unplugged.

Now, however, it wont turn on whatsoever.

Sometimes, when you push the button, the light will turn on for a split second, then go off.

Aside from a dead power supply, any ideas what it could be?