My friend bought a 5870 about a month ago he started recently having problems with it so he ships it back and they sent him another in about 2 weeks. He said that this one is even worse. Could it be that his bios needs updated? Sorry I don't have much detail.
Actually yes he did have a nvidia card b4 it I think he at least put the cards in and out about 3 times once to actually try it out second to ship it back and third time to put it in again. So he probably messed it up even more