Take the 2-minute tour ×  I installed gnome-shell and attempted
to log in to a Gnome session, but there is something wrong with
the graphics driver or something; all animations are accompanied
by a lot of fuzz, blocks of random pixels are everywhere, so I
decided to switch back.  Now the default Ubuntu session doesn't
start Unity any more. The only session that works as it is
supposed to is Ubuntu 2d. I've already followed the advice on
the other questions: Removed gnome-shell, gnome, gnome-fallback
and all associated with it, removed and reinstalled ubuntu-
desktop, and it did not help. Not sure what is going on here.
share|improve this question add comment  1 Answer  Why you
removed all? Unity is build on the top gtk3 so it may depend
some gnome components  try to reinstall unity  share|improve
this answer unity is installed. Per your suggestion, I have used
apt-get -f to remove it without removing a hundred other
packages, and then reinstalled it. Unfortunately, no effect. – 
Christoph Burschka Jan 26 '12