I have a Windows 7 Professional x64 machine, fully patched. Screen card is nVidia GeForce GTX 295. This card gets really hot, so initially when playing StarCraft II Wings Of Liberty I assumed it was crashing (sometimes 2-3 times in an hour) due to heat, as the sound still played, the screen went black and the machine was still pingable. Though I could not remotely connect to the machine or Ctrl+Alt+Del it, it needed a hard reset. This seemed consistent with the display adapter turning itself off to protect itself from heat, then being unable to reinitialise itself when it cooled down and causing the freeze.

I added a huge external fan temporarily, but it made no difference. In the end I found the problem - I had to revert to the Microsoft nVidia drivers, as any nVidia driver I installed from nVidia themselves caused the machine to crash.