Which Card you have.?
Are your drivers updated..to latest Forceware..?
Is the power supply enough...?
How old is the card..? Brand new..or second hand.?
Any OC'ing done.?
What version of DirectX you have..?
What OS..?
What games you trying to play..?
Which Motherboards you tried the card on..?
Don't panic..lets troubleshoot this baby....and get a fix..!