Just so you can exclude the driver being too old, I suggest you go to this thread[1] and get LinuxCoin. You have there a video tutorial and if you read on you'll see exactly how to create a USB disk from the ISO file (you can do it in Windows pretty easy). I can vouch that my 5830 xtreme can be overclocked to 1020 without BIOS editing, using LinuxCoin and the commands that I pasted.

If it still doesn't work, then it's hardware related and you might want to edit your BIOS.

1. http://bitcointalk.org/index.php?topic=7374.0