For some reason, my ATI Radeon HD 6850 (Known as AMD BARTS) only seems to work fine when I'm in a Live USB test environment. The driver's named "Gallium 0.4 on AMD BARTS", and whenever I finish installing the OS and reboot into its proper environment, I'm unable to log in due to a glitchy screen.
Something happens in the process of testing the OS and installing it that changes the Xorg/Gallium drivers. What can I do to ensure the same performance as I have in the Live USB environment? I tried downloading the proprietary Catalyst drivers, but they give me a myriad of other problems. I'm on Ubuntu 12.04 (x64).