It took several hours and a couple complete teardown/rebuilds , but I *think* I found the problem :
A Failing IDE device.
I'm not sure whether it was the cdrom or the HDD , both have been replaced , But the rig is happily folding away again.I suspect it was the hdd , it's an old one...I'll just centerpunch it and call it a day.
I'm not sure why the second rig did it , but that one is no longer in use anyways so...
24+SB cores , 7x Asus Strix 1070's ,storage, memory n stuff.Dual 4k monitor video .