Welcome to LQ!
From your description, I think you are booting to a graphical login screen. When you try to login, your /tmp permissions change is not allowing the GUI setup to write to the /tmp directory.
You could try booting to the login screen, hitting Ctrl-Alt-F6 to get a tty console, logging in as root and restoring permissions with 'chown root:root /tmp; chmod 1777 /tmp'. Hitting Alt-F7 should then return you to your graphical login and allow you to login normally.
Last edited by allend; 04-18-2015 at 11:46 PM.