"Under what circumstances will I need to do a reset?
Soft reset: Perform this reset if your have forgotten your password. A soft reset resets your password and disables security settings (Access Control and RADIUS settings are temporarily interrupted). Forgetting the password would normally prevent you from connecting to or configuring the AirPort Base Station or Time Capsule. If you make no changes within five minutes of doing a soft reset, the AirPort Base Station or Time Capsule will revert back to its former state. All of the AirPort Base Station or Time Capsule's settings will be available after it has restarted."
Perhaps try doing this and see if it works?