I was running Cinnamon, as usual. I had done a --dist-upgrade and installed an "AMD Catalyst driver" (ver. 12.4), during the session, to try and get my CPU fan to start regulating tempurature properly. My friend went to a fresh login, and Cinnamon failed to load entirely, though it appears as though X was still operating. The windows would open, without any frames. I couldn't select any of them, over others. There were no panels to click. Everything was f***ed. I tried rebooting and logging into my profile, and the same thing happened to me, with both Cinnamon and Gnome.
I tried booting to previous kernels. 3.0.0-16 would load the DE, with the wrong resolution, but 3.0.0-17 would react the same. I'm currently running 3.0.0-19. I've tried purging and reinstalling Cinnamon, with no results. I tried fixing broken packages, but no errors were found. I want to remove the AMD driver, but it came in a .run and I'm not sure how, other then delete the directory, and I'm not sure what damage it might do.
I'm currently running MATE, which seems to be running fine. The only thing I can think of, if removing the driver directory doesn't work, is to reinstall the '/' partition.