Ok I'm going to assume here that you've dled the 64bit drivers?
Did you DL the package with CCC or without CCC?
When I tried dling with just the driver files (no CCC) I got Black screen as well. The version with CCC worked for me so I kept it (you can uninstall later if you don't like it).
Another option is to remove and reinstall the drivers manually. Go to Device Manager and find your displayer drivers. Then go to properties and uninstall the drivers.
when reinstalling, you go to properties for your display tab (in Device Manager) and choose "have disk" and look in C:\Ati\... look into the directory with your latest driver files and choose the inf file you see which corresponds to the drivers.
I know it's a bit vague right now. If you don't understand leave a msg here and I'll give more detailed instructions.