The Ob desktop is back from the repairer. He’s pretty good, and looks like he might have identified the issue with the drives configuration referenced by software using certain core libraries, like Oblivion.
Did ask him if I could have solved it with a recovery disk (DVD probably, the old BIOS/UEFI doesn’t handle USB sticks all that well), he said probably, at the expense of wiping the disks, so yeah.
The Skyrim desktop was a mobo check and reseat, funny that as I thought it was fine. (And so it was. if looking at a blank screen was the desired outcome. 😛 )