Wrong on both counts. Both the PC and amiga could still be booted at least. Of all the OS's I ever worked with, only MacOS X has refused to boot from any device just because there is a HD in the system that is having trouble.
I've had a 40MB scsi drive that did much as you explain, but on my Amiga. With it plugged in, the machine would lock up part way through booting. When it was unplugged, everything was fine. Not having any backups and without a way to get anything off it, I just put it aside.
Later, the same drive had the same effect on a powermac 8100. It would boot, but lock up when trying to query the scsi bus. That was enough of a hint to me that the drive was screwed up in an electronic sense, and I threw it
In any case, if you need data off the drive (or to satisfy curiosity - perhaps format/resurrect it) stick it in a PC and see if it can avoid the problems the mac is having. It may cause problems there, or may not.
