Last night, I tried overclocking my XFX 4890 with ATI's Overdrive. I bump the core speed from 850 to 900, then I entered BF3 and noticed a lot of artifacts before it soon crashed. I was going to restart my computer and set it back to defaults since it was clear I wasn't going to get crap out of overclocking this card (I got it after RMAing another 4890); however, when I got to the windows logo just before login (Windows 7), I get a BSOD every time. So then I tried to boot in safe mode, but the same BSOD happens. Any suggestions?
Oh, and I forgot to mention, I just had also just updated my video card drivers minutes before. The BSOD says, "BAD_POOL_HEADER" and "Stop: 0x00007e". Upon googling that term, it seems it is a driver issue instead of an overclocking issue.
If it fails to boot in safe mode, you could try booting with a different card / onboard video, and remove the driver that way. If that fails, i'd try the card in a different system and see if the card is still okay, and if it is, you might be looking at a reload of Win 7.