I was running Ubuntu 9.10 (Karmic Koala) with no problems. I recently upgraded to Ubuntu 10 (Lucid Lynx) and cannot use it normally. After I log in, the screen scrambles (a purple/green mess)--impossible to see anything, although I can get out by marking the spot on the screen to click for a restart, so Linux is working behind the scenes.
If I start in recovery mode with basic graphics, I have no problems at all (other than limited functionality). If I start the old 2.6.31-22 kernel, I see a bunch of "unmountable" errors in the startup script, but I can use Linux normally with no apparent problems. I'm running an IBM ThinkPad A30 with ATI Mobility graphics. Just to reiterate, the screen looks normal until I log in, at which point it goes bonkers.
What do I need to change in order to fix this?