How are you installing the drivers? Just updating right over the top of the old???
Ati have often picky installs of drivers...You normally need to remove old drviers and force the the card back to standard vga adaptor (default) the install drivers through update drivers in system devices...
Please list the drivers...Also try downloading it again from another site and see if maybe an error happened while downloading..
As per ATi's readme's I uninstalled the old drivers first. I get the same problem with the last two released driver revisions. The beta driver is no longer available on the ATI website. I just bought a 8500DV and the beta drivers don't work with it.