Graphics messed up in games then freeze

While playing games, my PC crashed randomly. What happens is that my screen will start to flicker black & white (I think) and suddenly my game's graphic is "broken" and my PC froze. I have to restart it again. And oh... I got a blue screen of death once. Weird thing is, it was only once out of so many graphic crashes.

Even if I do manage in time to alt + tab and End Task my current game, the black & white flicker remains until I restart my PC.

So far I've eliminated these possible causes:

PSU - I'm using 650 watt PSU and my graphic card is GeForce 8600 GT. It is more than enough and since I've been using the same setup for nearly a year now, I dont think it's PSU. I've also cleaned to make sure accumulated dusts arent the problem.

GPU's fan - I've tested my GPU using Fur Rendering test. The fan speeds up appropriately to keep temperature in check.

Drivers - I've uninstalled the graphics drivers, used Driver Cleaner tools and reinstall the latest graphic card driver for my GPU. So I dont think this is the problem.

Specific games - I crashed on nearly all games that are 3d. The only ones not crashing (so far) are Football Manager and X3: Terran Conflict. However I dont think those games utilize GPU that much anyway.

RAM - Unless both my RAMs are busted, I dont think this is the problem. I've tried using 1 RAM then play a game but it still crahsed. I tried the other RAM and no good still.

The only thing that comes to mind is motherboard. However I'm not sure how to test that it is really the motherboard's fault and if it is, how did it become faulty?

 

There is no game crashing.. just computer lock-up So when I play a game, sooner or later:

1) graphic freeze
2) black & white screen flicker
3) loop of the last sound the game made
4) I can still move the mouse but it seems at 1 fps (laggy)
5) eventually the whole PC is locked up. I cant move my mouse anymore etc
6) restart

I've also eliminated two more possible causes: monitor & hard disk space