Comment 6 for bug 1066410

Same problem here (12.10 64Bit).

Restarting lightdm didn't work for me. All I got was this black screen with a blinking cursor. To get to a working desktop anyway, I (temporarily) switched to gdm by doing:

1. [alt+f1]
2. $ sudo apt-get install gdm
3. restart machine. when gdm loginscreen comes up, select ubuntu (instead of system defaults).

To switch back to ligthdm, when its working again, you can run:

$ sudo dpkg-reconfigure lightdm