Frontline: Fuel of War shuts down my PC!!!!

When playing FFOW online, my PC shutsdown within 5 mins of starting a game. This doesn't happen on single player, or with any other game. My temperatures are fine and stable throughout, the game is fully patched, and there are no indications of any faults until the PC switches itself off. I am running Vista Ultimate 64, Quad Core CPU, 8800GTX with 4Gb RAM. Any ideas? Thanks in advance.