I agree with jaguarskx that you should test with some other 3D game (possibly a free demo, e.g. from Steam if you use that). For it to happen right away rather than after the card has had a chance to heat up makes me hopeful that it is a software issue rather than hardware. Also, as wintermint says, if you've overclocked the GPU, back it down to stock.
What brand and model (not just wattage) of PSU do you have?