I had the exact same problem (Windows 7 Pro 64 + 8800GTS). It all started a couple of days ago, and I noticed that when I played heavier games thy crashed. At the begining I was suspecting a bug in the game, but then I noticed the exact same problems when I was running other graphical-intensive software.
My first thought was overheat. And that is strange since I like to believe that I have a oversized cooling system in the case, with many fans, etc. But what the heck? I opened the window for extra cooling effect (winter, right?). It was slightly better but still it crashed. That led me to think I have a serious cooling problem.
However after investigations, the temp seemed not to be the root cause (rather a side effect). So I started looking at the drivers
. My luck (or bad luck) was that I just performed a rather tricky SSD firmware upgrade and I thought it was giving me the errors.
So after days of pain, I decided to reinstall my Windows 7 completely. Did that, but immediately after installation, same problems. Ooops... so it wasn't because of old OS installation. Then, downloaded the latest nVidia drivers from the net (195.62 WHQL), did a Windows 7 reinstall, afterwards immediate driver
upgrade and zap. Same thing.
At this point I was really upset. I opened the case, cleared all the dust, rearranged the cables for better air circulation, did a full RAM test, HDD test, etc. Nothing everything went OK.
One more try, who knows? Everything went fine, then Windows 7 asked me about the nvidia drivers automatic update, said OK, and ZAP!! Whooow... wait a minute, we're getting somewhere. Again Windows 7 completely unusable (not even managing to boot without a crash).
Again, reinstall. And said NO to the nVidia drivers update. Also I didn't install the latest nvidia drivers I had downloaded a couple of reinstalls before. And everything works as it should. Currently I have the NVIDIA GeForce 8800 GTS version 18.104.22.16893 (that came with the Windows 7 installation kit) released on 14.05.2009.
I hope this helps someone!
And Marry Christmas!