Try using driver cleaner to get rid of the rest of the ati drivers and use the newest ones from the site. My card runs real good. Destroys my old 7950gt even when that was at gtx speeds and with some aftermarket cooling, you could push this 3850 to 3870 specs.
If after a complete driver reinstall, check the voltage on your cpu and temperatures. If you still cant get it, return it for a sapphire 3850 or just get a 8800 gt.