In the two systems I have this has happened to me when upgrading: the former video drivers are kept (under packages named xorg-xserver-driver-xxxx). If you manually select the package xorg-xserver-video-all (note the change from driver to video), all old versions are deinstalled, new ones installed, and X resume working flawlessly.
-- Can't calculate the upgrade with unofficial mesa/compiz packages https://launchpad.net/bugs/58424 -- ubuntu-bugs mailing list ubuntu-bugs@lists.ubuntu.com https://lists.ubuntu.com/mailman/listinfo/ubuntu-bugs
