Suggestions and questions for you. All require an OPEN case as minimum.
(1) Check the SCSI cable connections? Was it loose? Re-boot!
In the past, and in an emergency, this can work.
(2) Use a rubber mallet, or rubber handle on a hammer. Tap on the drive's center AS it powers up. Does the drive spin and whirl? Any repeating clicks? Did it boot-up? If so, copy files, as this is NOT a fix.
(3) remove drive. Put in refrigerator for 24 hours. Re-install drive, and re-boot. (not a fix, and if it works, may work only 2 hours).
The jaz was not set up as a boot drive, but you can boot from the workbench disk, with the jaz connected. The jaz icons should appear on screen after you toggle "backdrop" from the workbench screen.
As I do not drop-by that often, you can email me, if needed.