I used to use Guake terminal. When I was using last time Guake stuck and stop working. Pressed F12 several times in order to close the terminal. Then system logged off and login screen shown up. Entered password for my username couldn't log in. Tried to login with Guest mode still couldn't log in. Then I googled, found some solutions: Ubuntu gets stuck in a login loop. Then I tried to log into shell using Ctrl+Alt+F1 entered username and password still couldn't log in. Tried to get into recovery mode using this link How do I boot into a root shell?.
But 
didn't show up.
I have no idea what to do!
How can I solve the problem?
