Just have been playing LFS, and my monitor blanked out, the GPU fan started spinning at maximum speed, and I could not reset it, I had to unplug the PC from the socket...first time that happened.
After I managed to restart the PC I checked the GPU and CPU temps...all normal. Tried playing LFS, rfactor, portal - did not happen again so far.
PC specs: Athlon X2 64 6000+, ATi 3850, ASRock AM2XLi-Esata2 mobo, corsair VX450 power supply, Win XP SP3, all patched, all latest drivers, no viruses or other shit.