Vista - Vista screwing up big time.

Well i'm not entirely sure it's Vista screwing up but I believe it is since it can't be anything else.

I have a Gateway P-6860FX

4 gigs of ram
Nvidia 8800m GTX (512)
Vista x64

Right now whenever I play games (x64 compatable ones) my computer will freeze up after a few minutes of gameplay. I noticed it freezes particularly when I open a new screen in-game or click on something that will result in a drastic change on screen (For example opening a menu mid-gameplay) When it freezes I can't even Alt-Tab out of the screen or even open the Task Manager. I have to improperly shutdown, and recently, the computer won't even start up, bringing up the startup repair permanently. I took it to Geek Squad and they ran a Diagnostic only to find all hardware to be running perfectly fine. I restored the computer to factory set up, and am currently installing the game again to try it once more.

What could be causing the freezing?

Any number of things, such as improper drivers, corrupted files, bad sectors, failing RAM, failing video card ram, etc....