I have a Dell PC in the garage which dedicated to driving my CNC lathe and which was bought second-hand off a well-known auction site. Works a dream, except every couple of months it fails to boot and the flashing LED shows the code for “memory configuration error”. Switch off, pop off the lid, swap the two memory modules, lid back on, reboot. No idea why but it seems it’s a known problem. Works every time, even though the same memory modules are cycling between the same slots on the motherboard. Like Michael’s disk problem, probably a contact issue, I would guess. Switching off and reseating every plug (including the CPU once) has fixed more than one problem for me.