IBM thinkpad R31 problem

I am thinking that if there were a board fracture or other board
problem, it would not start or run reliably at all and simply go
unexpectedly black, especially if moved or the case is flexed. Have a
look at the cabling, especially around the HD since this is where it all
started and remove and reinstall the RAM. Check for a loose or
improperly inserted cable. The restart halt might point to a loose
cable to a device that the OS is polling for and lifting the side
momentarily makes the cable contact. You could try stripping it down to
one RAM stick, the HD, no other cards, drives or network connections and
see if you can narrow the problem to one device. After startup, are
there any devices going missing in Device Manager? Does BIOS setup look
'normal'?

Did the drop visibly damage the case?

Q

From what you say, I would say there is a crack in the MB. Some contact
gets broken when the board expands with the rise of temperature. It
would probably take a microscope and a lot of luck to locate the crack
(assuming there is only one), not to mention being able to repair it.
But you might get lucky ...

--
John Doue