OS and Mobo, Mobo and OS

Jim Cockfield wrote:

That would be my best guess (PSU has degraded over time, as they usually will).

I'd make sure to reseat everything you can (memory, drive connections, video card, etc.), just to make sure everything is getting a good enough connection, too (in case a bit of oxidation has built up over time, since reseating the connections can help to remove it from the friction of the contacts rubbing together).