GTX 285 problems :(

MB: EVGA Classified x58 3 way SLI
CPU: i7 920 / Antec Kuhler h20 920
GPU: EVGA GTX 285 (with most recent drivers)
RAM: Mushkin Enhanced 24GB (6x4GB) 1600 DDR3
OS: Win7 Pro 64 bit
PSU: Corsair HX620

Sometimes (practically only in GW2) my screen will go black and I will have to hard shut down and turn my computer back on for anything to work again. Sometimes I can still hear audio playing (ex. skype and can still talk) while others I'll hear the .01 seconds of whatever was playing repeat itself. My keyboard lights also turn off. It only happened a few times (3 maybe?) while playing WoW, but then when I started playing GW2 it started happening randomly between 30mins and 4 hours of playing. Now it seems to happen between 10-20 minutes of playing, making any effort to play GW2 futile however WoW doesn't experience this problem aside from the few times its already happened. My CPU temps are perfectly fine, and my GPU temps never go above 75C (fan speeds are adjusted in EVGA precision X fyi). What might be causing my problems?
EDIT: I've turned off all of my OC btw and the problem persists.