Created attachment 63722 [details] error log I've tried updating ubuntu and installing it again (fresh install). X doesn't starts and I open a new terminal session with ctrl+alt+F2 but when I try to reboot the system, it crash. Sometimes (I don't know why) the driver loads OK (1 startup ok -> 5 startups ko) I attach the dmesg error. There are a lot of files of information in https://bugs.launchpad.net/ubuntu/+source/xserver-xorg-video-ati/+bug/799252
According to the linked Ubuntu issue this bug was fixed between 2.6.38 and 3.0. Unless someone wants to identify the fix and backport it to an earlier longterm release I propose that this bug be closed.