suspected hard disk problems
I had a quit simmilar issue on same 7300-8500 OldWorld.
This arise when tried a installation "after" an "reboot" from MacOS.
This "reboot" put the mac-box in ro - read-only - statement,
but the d-i work correct, this mean there are no any errors message ,
and so, after reboot in new debian system, almost all
directory are only ro !!! Nice !!!
The solution was to use "shutdown" from MacOS
and a new power on "before" the new installation - d-i.
I've heard what sounds suspiciously like the "click of death" that
hard drives like to make before dying.
This all was ok in the "right" mode of booting.