Ubuntu 15.04 boot hangs on "Starting light display manager" after updates
Solution 1:
Try to go to tty1 (Ctrl+Alt+F1)
Login and purge xorg and lightdm
sudo apt-get purge xorg lightdm
Autoremove whatever's left
sudo apt-get autoremove
Install lightdm and xorg
sudo apt-get install xorg lightdm
Solution 2:
There is an easier solution I think.
Try from client ctrl-alt-f2 (F1 might not work, as it is trying to boot)
Then run
sudo dpkg --configure -a