Switching to 32-bit won't help you, I'm sure of that.
* Is there a message when you try to login?
* Try loging in on terminal, what error is there?
* Can you log in as root?
* Run from live-DVD, check the partitions you have so they're not full. Also check the logs from installed system.
Last edited by pingu; 03-17-2013 at 11:20 AM.