I have lubuntu 12.04, and it was working fine until I installed something and I do not remember exactly what I installed because I was trying to build a ruby gem and it required a lot.
now I rebooted and I cannot log in, well, I can but when I do LXDE apparently cannot continue and returns to the login screen.
I created another user from my console screen (I can login there), and the other user can login. So I removed my .* directories from my home directory, but it did not help.