Be sure that you have:
* Connected the drive to the 50-pin SCSI connector instead of the DB-25
port serial connector on the I/O board.
* Not connected your computer to the same SCSI bus as the printer and
the hard drive.
* Let the drive become ready before turning on the LaserWriter IINTX.
If all the above are correct, you may have a bad LaserWriter IINTX
controller or hard drive mechanism.