I am running ubuntu 14 on a mac machine. recently I notice compiz was too slow, so I changed from default generic driver to propietary. after that, I got a blank screen.
I am able to enter recovery mode, and even launch the dialog to configure graphics, but it is unusable (it did not respond to keyboard nor mouse, so no way to select any option there).
I had tried many suggestions in the forum, (reinstall compiz, unity-desktop,purge nvidia drivers, reconfigure xserver-org..) but most of them seems to be for older versions of ubuntu (by example, I don't have a xorg.conf file) so I wonder if there are fresh instructions specific for ubuntu 14.