i had a strange issue a while back, my gf/s pc gpu did this, only a 7600gtx. it worked in my pc tho, and my 5770 worked in her pc. bought a new mobo (amd chipset) for her, same problem, tried a different nvidia card in hers still didnt work, bought a 5450 for her and it works fine,
this was an amd 3000+ cpu on a nforce chipset mobo. so ruling out the mobo and psu. i think it was a fault with the cpu.