This is what I have done to fix ATI video problems in the past if the OS is not corrupted or if there isn't a virus or malware issue. First download the latest driver
for you card to your computer from ATI not Windows Update. Then completly uninstall the video card drivers
and the Catalyst Control Center. Restart your computer if it says to, next install the new drivers you just downloaded. You may need to Run as administrator to install the drivers even if you are the admin .
I have an 4870x2 and it ran great in the RC and in 64bit Ultimate RTM.