Gaming Rig is crashing under pressure

I built a gaming rig back in the summer and it ran beautifully until I stopped using it once school started again. I recently noticed that when I try to run games like crysis 2, max payne 3, or just the heaven DX11 benchmark, my screen will form colored boxes all over the screen, and crash. It says some business about 'stopped working' and takes me to desktop.
I have updated all drivers and have made sure my OC is at a reasonable 4.2 ghz for now...I have precision x gpu monitoring software and my comp has about seven fans and an H100 so i don't think its a heat issue, as my temps don't exceed 60*C...I use a single EVGA gtx 670 FTW edition and fear something may be wrong with the card...comp works fine when not running intense games (i.e. can play diablo 3 and skyrim) I'm getting kind of exacerbated by the whole thing as I haven't gotten to play BF3 in a while or any of my other intensive games...any suggestions are more than I can come up with right now, so feel free to drop any advice you may have.
thanks in advance,