I was in Ubuntu (Unity 3D) 11:10. I was using gnome tweak tool to change my
themes. Suddenly I got kicked out to the Login screen. Not the lock screen.
When I tried to login it blanked the screen for a moment (complete black screen)
as if it was going to login and went back to the login screen. There is some
text that flashes after the screen goes black but it is too fast to read even
part of it. It's white text on black like command line in the terminal.

I have tried logging back in under Unity (3D), Unity 2D, Gnome classic (no
effects), Gnome classic, and Gnome 3. I get the same results each time. I used
the guest account, created an admin level user using the password of the account
that I can't login to, and logged in with no problem under the new account.
Everything is fully functional under the guest and the new account including
gnome tweak tool. So the guest account and the new account are unaffected.

Thanks to everyone for all the suggestions and help. It's greatly appreciated.