Do not under any circumstances enable the PowerBook 3400 password security if you have At Ease 4.0.x installed on the PowerBook and you have enabled the "Prevent users from bypassing security by starting up from a floppy disk" option in the At Ease administration program.
The hard disk driver becomes corrupted in such a way that the PowerBook is unable to start up. Additionally, the computer will not start up from a floppy disk, CD, or in SCSI disk mode.
Apple is investigating the problem and working on a solution.
This article was published in the 23 May 1997 "Information Alley".