I updated to 14.04 by reinstalling over the old 12.04 install.
After using the system for a few weeks I log in one day and there is no desktop / unity at all. Just a background and mouse pointer. The guest session logs in fine.
I've tried various posts (Problems after upgrading to 14.04 (only background and pointer after login)) etc but it seems I'm shooting in the dark...
In the syslog there are errors about compiz.desktop killed by signal 9 and respawning too quickly but I can't see any fixes for my case.
I should add that a guest session logs in fine and the unity desktop displays as per normal...
Can anyone shed any light on this?