I have a hamm system here that I can log into, but it kicks me back to the login prompt after it displays the default Debian MOTD, and the "No mail" message. It does the same for every user, including root, even in single-user. I've wiped the drive and reinstalled Debian twice from a hamm CD and the current disks, and I still can't login. The system was originally an unstable system, upgraded a week or so ago, but this just started two days ago. Any clues?