Morning AdventCalendar, sorry about that. Memory comes in what we call sticks, and you can have one or more in your PC, IE: 1x256 or 2x128=256 or any combination to make up the amount of memory in the PC.
If one is faulty, then you can check for this by doing the above.
Will you also please confirm if the PC is sticking on all programs, or just on defrags and scans. J.
AdventCalendar, my first thoughtr was that this is a software problem - but then I read your original posting more carefully. If you can't reboot for 5 to 10 minutes, it has to be an overheating problem. There is nothing else in the computer that retains any memory after switching off. If after switching off you can't even get to the black and white boot screen, then I would suspect processor overheating. If you can get this far, but cannot load Windows, then I suspect hard drive overheating. The first symptons you mention also point to hard drive problems, so it could be that the hard drive is developing a fault or that your friend needs a hard drive cooling fan.