This question already has an answer here:
Same Problem: Ubuntu 12.04 LTS. Returns to the login screen in all GUI modes despite I enter the correct password.
Solution found in this blog -
Log with Guest user
Ctrl+Alt+F1 to log as I couldn't log before, or if preferred as root.
rm /home//.Authority to remove this file
Ctrl+Alt+F7 to go back to Guest session and try to log as >>>> SUCCESS
THANKS A LOT TO EVERYBODY AND SPECIALLY TO Lili