Recently I update my Ubuntu 11.10 to Ubuntu 12.04 . I have 2 user in previous Ubuntu and was able to login as root from Ubuntu Gui. In Ubuntu 12.04 by default other account has been disabled by Ubuntu regarding security purpose.And its quite true that Login from root may crash or damage your system. Though risk I have enable the root login from Unity for certain purpose.To login your system from root user in Gui You need to change a couple of lines in lightgdm sytem file. I have used Vim Editor to open the open. The file is in
and add “greeter-hide-users=true” this line to above file. Your file should look like this now.
Then Reboot your system. The login screen should show like this in pic. Now put root in username and your password in password field.