Just exactly what mine did my friend, I had a powercolor X800XL cracking card then one day it started dropping out to black screens/locking up etc. As yours is it started doing if more often. Then it died .
Took mine to the shop along with the original card the machine came with 2.5 years later, not under warranty anymore but the nice people tested it and stamped R.I.P on it and reinstalled the original card, all for free.
There are some decent companies out there still
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