After playing with bumblebee and bbswitch on my Asus U36S (Optimus, using the free graphic drivers), I broke my graphic session on my up-to-date LMDE MATE 64bit (March 2013):
- no login screen (just a prompt to log in, and startx did the job)
- after several reboot without changing anything, my MATE desktop changes completely and I got something looking like a giant smart phone (I did not install any alternative desktop)
So, not being able to solve this problem, I re-installed my LMDE yesterday evening. After having applied the updates available (and reboot) and installed my usual packages (nothing linked to xorg, graphic drivers or desktop), everything was fine. Then, I shut down three time my laptop (just normally, without installing anything else) and the login screen disappeared again. And I'm know afraid that the smart phone style desktop come back without notice.
I don't know what it's causing that. In the same time, I installed the exact same ISO on three desktop pc without any trouble so far. So, if anyone has a hint of how to recover the login screen and what to check or correct, I will be grateful.