Same as mine,, Win 8 Pro x64..
Ok do this..
go to c:\windows\system32\DriverStore\FileRepository.
there will be a folder named '' ati*something*something* ''
just rename the folder to some thing else.. but remember to take a note of the actual name of the folder.
by doing this,, it will not install the default Ati Driver when the gpu driver is uninstalled from the Device manager.
Then go to c:\windows\inf\
There also you will find a file named '' ati*something*something* .inf ''
rename it to something else.
now open your Device Manager and uninstall the GPU Driver.
Select the option of 'delete driver files' when uninstalling.
Now reboot.. your pc should be booting with the Basic Display driver and not the default ATI driver..
then go to Device Manager and update the Basic Display driver Manually with this Modded Driver.. It should install nicely...