Un-install the current drivers you're using.
Then get Driver Cleaner Pro (it's free, google it), go in Safe Mode (un-install the drivers in Normal Mode before that). Now run the cleaning tool by clicking "ATI", and only that, nothing more in needed. Start the cleaning. Wait until it's finished.
Now reboot in Normal Mode, run Driver Cleaner again just to be safe, and install another Catalyst version.
I highly suggest Cat 6.7. Cat 6.8 seem to cause a few issues to some users (it's a minority, but you might be part of it, personally, I am having issues of all kinds with 6.8, others are fine with it, you'll have to test if you want to be sure).
Hope it helps.