The system is operating in SCSI Disk Mode (HD Target Mode), which is not what you want. See the PowerBook 1400 manual (
here) for details.
The square plug of the cable (or a separate adapter without a switch) should have 29 pins if used with an external SCSI device (such as a hard drive). Alternatively, if an adapter with 30 pins and a switch is used, make sure that the switch is in the correct position.
Jan