Game Freezes, Audio loops, PC crashes.

Just at the subject dictates.

I play just fine on most servers, though once in awhile (regardless of player count and particles on screen, last time it happened i was looking into a wall) the game will totally freeze, becoming unresponsive to any keyboard command, (Alt+F4, Ctrl Alt Delete) And then "poof" Black screen.

This is a totally random incident, it happens "when it wants to happen". Sometimes i can play for hours on end on pressure heavy levels. I've ruled out overheating as im running a custom watercooling loop, double checked pump, fans, temperatures and waterflow. I'm thinking it might be the PSU but it feels like it wouldn't freeze the game first before crashing.

Anyone got any ideas?

Windows 7 ultimate

Intel i7 975 @ 4ghz

16gb ram

580GTX sli.

1200 w powersupply.