Stucked in your desktop/laptop ubuntu’s login screen means , you enter your password then screen goes black then login screen appears again and again in loop , here are three easy troubleshooting methods you can follow to resolve your problem.

Error Info

$ cat ~/.xsession-errors

now see and identify what is causing the problem .

Method 1

Login in console mode using ctrl + alt + f1 or ctrl + alt + f2 then

$ chown $USER:$USER .Xauthority

if it doesn’t work try renaming .

$ mv .Xauthority .Xauthority.bak 

Then press ctrl + alt + f7 to go back to login screen , if these all solution doesn’t work , then uninstall and install again lightdm

Method 2

# For re-configuring
$ sudo dpkg-reconfigure lightdm

Re-installing

$ sudo apt-get purge lightdm && sudo apt-get install lightdm

Or install gdm in place of lightdm

$ sudo apt-get purge lightdm && sudo apt-get install gdm

Screencast

I hope it was helpful for you , thanks for reading .