Ubuntu stuck on login screen [duplicate]

I have a small issue with my Ubuntu (I think After an upgarde). When I try to login (Login Screen), I get disconnected and get back to the screen (again & again).

I tried:

• Trying to login with others Desktop environements.
• Booting from old kernel.
• log in via command line [apt-get update && apt-get upgrade].
• removing ~/.gconf directory.
• sudo apt-get install --reinstall ubuntu-desktop and sudo apt-get install unity

None of these solutions worked.

Press Ctrl+Alt+F3 and login into the shell using your username and your password. In this case username will be your username you set when you installed Ubuntu.

Now run ls -lah and look for the output line that ends with .Xauthority

-rw-------  1 root root   53 Nov 29 10:19 .Xauthority

then you need to do chown username:username .Xauthority and try logging in.

Else, do ls -ld /tmp. Check for the first 10 letters in the left: they should read exactly so: drwxrwxrwt.

drwxrwxrwt 15 root root 4096 Nov 30 04:17 /tmp

Else, you need to do sudo chmod a+wt /tmp and check again.

If not both, I'd recommend you either
Make sure you are connected to internet with DHCP on.

1. sudo apt-get purge lightdm
2. sudo apt-get update
3. sudo apt-get install lightdm
4. dpkg-reconfigure lightdm

Now type sudo shutdown -r now to restart.