I was using Ubuntu 12.04 perfectly on my desktop until last kernel update (3.2.0-51). After the update process and reboot of the system, the Unity interface didn't start. The only way to login in the system is by tty. I have tried the last kernel versions available in the computer, but I can't use the graphical interface.
Until the text terminals is impossible to access the unity interface.
If I don't find a solution I will re-install the whole system.