I have the same problem with a Sapphire Vapor X 5770. Tried so many different things I got so desperate I tried checking the brightness. Still on onboard graphics, I'm going to try the card on a different PC sometime tomorrow or later on, you should try that too and see if it works. If it works on another PC, then it's not faulty or anything, and something is probably not working properly on your other parts. I've been asking around so much on different forums but people rarely reply. I guess no one knows lol.