Them are software related problems, it has nothing to do with your GPU. If it was your GPU you would get artifacts, driver crashes, and other various stuff. It has to do with your software configuration or your processor. First thing I would do is eliminate all possible cases of it being a hardware issue. Download
Prime95 and
CoreTemp and run a stress test on the CPU (e.g. In-place large FFT's). Monitor the temperatures to make sure your processor is a) remaining cool and b) getting enough volts. If you can pass 1-2 hours of Prime95 than its not your CPU. Which means its a software issue, e.g. something conflicting with the game causing it to stop responding. If you want you can also download
MemTest86. Burn it to a CD and boot into it. Select the first option (single core) and let it run for 2-3 passes. Memory is very fickle stuff, if it doesn't error then than its likely not going to any time else. With all of that done, you can safely say its a software conflict. Tho I can ensure you that its not your GPU.