I have recently been experiencing issues with my GPU. A while ago, it stopped detecting my primary video card, so now I'm using my onboard. I had a power surge earlier today while the computer was on. It turned off because of this, so I booted it back up only to discover that it was detecting my video card again. There was another power surge later in the day, and I rebooted to find out that it was no longer detecting my main video card. The initial problem with the GPU was that it wouldn't send a signal to my monitor, but the fans on it would power on.