It sounds like you're most of the way there. You'll probably find it easier to troubleshoot this on the command-line, where the errors are more informative.
Perhaps try this command, which performs a login and does nothing else:
(Note that your domain should always be in uppercase for Kerberos).
If this fails to login then the problem is with the configuration in /etc/krb5.conf. If this succeeds, and running "wbinfo -u" returns all the users on the domain then Winbind is OK, and the problem is elsewhere.
You haven't specified how you are trying to login, so I'm assuming you're using the graphical login screen ?