After upgrading to Quantal yesterday I installed the new ATI Catalyst drivers, the 12.10 version, for my ATI Radeon HD 7850 card. Upon logging into Ubuntu I am presented with no Unity. I can access terminal with Ctrl + Alt + T.

I tried uninstalling the driver, but that did not fix Compiz.

Does anyone know how I can fix Compiz? Any info on getting drivers working would be good too.

Edit: I solved this problem by first uninstalling the proprietary driver through the terminal, which I believe is in /usr/share/ati/amd-uninstall.sh. Then I rebooted and installed the open source driver, radeon, and rebooted again. It's slower than the proprietary drivers but it works.