you can try the card back in XP to test to see if it's working.
if not working then you will know it's the card that's now bad and not the compatibility with win7.
i have a hd5770 but not powercolor in win7, so it does work.
In winxp it is working beautifully with best possible performance. But windows 7 I am struggling to get drivers installed, which is not happening. I tried with original CD, drivers from ATI-AMD's site and Powercolor's site. I will check once again with clena windows 7 install and post on this thread. Thanks.