My Quadra 840av dont boot from any SCSI-Devices at boot.

When i boot the Mac OS 7.5 floppy, the apple drive setup tool say that the harddisk doesnt contain any valid partitions, and it cant format it. :'(

I test it on the internal and external SCSI-Bus, with ZIP100 and my 2Gb Harddisk from the Quadra 700 (my Quadra 700 can read and boot from the DIsk)