A howl on the wind…

In order of importance:

• Run the game with your computer cabinet open to mitigate possible overheating.
• Clean inside your cabinet. Dust may be preventing your fans from turning.
• Test your memory with Memtest86 from http://www.memtest86.com/
• Test your CPU with Prime95 from http://www.mersenne.org/freesoft.htm
• Update your drivers.
• Reset your BIOS settings to factory default.
• Reset your BIOS settings to safe mode, if possible.
• Open both cabinet and use a window/fan/whatever to really make sure overheating is not the issue.
• Swap around internal power cables. Could be the one that goes to your GPU is overloaded and doesn’t feed enough power to maintain it.
• Could be your PSU is generally overloaded. Unplug any device that you are not using. If you have 2 HDDs, remove the excess one. If you have any unused PCI cards, take them out.
• At this point, pray. It could be anything and you need to do an individual component check, but it is most commonly the PSU that’s the culprit.
• …if all that fails, report back when you find what exactly was wrong.