Here are the facts:

    * I ran some stress-tests last night.    
    * I forgot to reset the logs to minimal.
    * When I got this morning, I saw that hard drive is full /dev/sda1.
    * Cleaned up the large file (350GB).
    * I experienced the machine being a bit slowlier than usual.
    * I rebooted the machine.

If I provide the wrong password on purpose, it shows the usual error. When I provide the right one, it is like an infinite loop.

When I hit Ctrl+Alt+F1 and login at tty1, for instance, all works fine.

From tty1, I tried to setup auto-login as follows:

    sudo vim /etc/lightdm/lightdm.conf
    autologin-user=<username>
    autologin-user-timeout=0

I also tried `startx` from tt1, re-installed `gdm`, `lightdm` but with no help. All I see is an error at /var/log/lightdm/lightdm.log that the process gdm-greeter get killed

[1] http://askubuntu.com/questions/256344/cannot-login-to-my-machine-using-the-right-password [2] http://serverfault.com/questions/479126/cannot-login-to-my-machine-using-the-right-password