Comment 13 for bug 226993

Your installation is hosed somehow by the upgrade. GF8600GT works just fine here. The log shows that it's using the vesa driver, which means that the driver failed to load either because the nvidia kernel module can't be loaded or because there's a version mismatch between the kernel module and the X driver/libs.

Shut down GDM by running '/etc/init.d/gdm stop', and then from the virtual terminal run 'sudo startx'. That should give you the real error. Make sure to have 'nvidia' in /etc/X11/xorg.conf before you run startx.