Interesting to say the least. I remember when I flashed an AMD 5850 With an OC BIOS. After that nothing on screen..but the PC was booting. I then took the card and put it in another system, Bam it was working fine. I then put it back in my original system and again no picture.
I reset the CMOS, Re-flashed the Mobo BIOS but nothing worked. So I put it back into my second system and flashed the stock BIOS back to the 5850, put it back in my original system and it was working fine again. No matter how hard I tried my original system refused to show anything on screen with that custom BIOS.
Both systems had the same PSU so it was not a power issue and generally speaking would not be anyway as it used minimal power on posting.
I never did solve it...it was one of those random gremlins that did not follow any logic. You get it sometimes :(
I hope you get a better card back !