| posts: 1,240 | Location: New Zealand
So back up a little, did you install over the top of your 10.6's? or did you driver sweep from the beginning?
Honestly, i've stopped using driver sweeper for ati cards, i've had it mess up things too often. Have you tried uninstalling your drivers through device manager? if not, give that a go, reboot then try the installation of 10.8 from there.
Theres a possibility driver sweeper has screwed someing with your OS, some time back I had a problem where I could only play games in dx9, not dx10 or 11...this was caused by two things, betas drivers and/or driver sweeper. I had to reinstall all of my Microsoft C++ files to fix this. Perhaps those same files are at fault for you.