This is sounding bad! So,
1. Press Alt-Ctrl-F2 to get a session without a GUI and you should be able to log in as "root", giving your root password.
2. Check that it has created a user directory in /home with
If there's nothing there, it didn't create a user. In that case, do it with
and set the password with
and give your password when requested. Then Ctrl-Alt-F7 should take you back to the GUI.
2. If it has created a user, reset your password with the "passwd" command and see if that solves the problem.
3. If it still doesn't work, come back and tell us.