Fresh user profile

Log out, open TTY 1 (CTRL-ALT-F1), log in with your p-number.

If you want to save the dot files, you can do this:

mkdir ~/backup_dot_files && mv ~/.* ~/backup_dot_files/

NOTE! this will give you the following error message that you can ignore:
mv: cannot move '/home/p123456/.' to '/home/p123456/backup_dot_files/.': device or resource busy
mv: cannot move '/home/p123456/..' to '/home/p123456/backup_dot_files/..': device or resource busy

If you have no settings you want to save, you can do this:

rm -rf ~/.* 

NOTE! this will also give you an error message that you can ignore:
rm: refusing to move '.' or '..' directory: skipping '/home/p123456/.'
rm: refusing to move '.' or '..' directory: skipping '/home/p123456/..'

The following directories containing most of the application settings you did yourself. If you want to keep your settings make a copy of these directories:

• .local/
• .config/

After cleaning your profile and logging in works again, you can copy back these two directories the same way you removed them; Log out, open TTY 1, log in with your p-number, copy the directories and login to graphical user interface (GUI). If the trouble returns, the problem is in one of those directories. Clean your home dir again and now copy back your settings one at a time to find the culprit. I also made a, in no way complete, list of directories you might have in your home dir that are sometimes the cause of trouble and you can delete without thinking about it twice:

• .dbus/
• .gnome/
• .gnome2/
• .gnome2_private/
• .qt/
• .nv/
• .nvidia-settings-rc
• .Xauthority
• .gconf/
• .cache/
• .kde/
• .compiz/

Switch back to your window manager (CTRL-ALT-F7) and log in again. If everything works again, don't forget to logout of TTY1.