Sounds like a case of "it's always the PSU" in figurative sense... e.g. half-blown fuses, dried up caps, good +12V but weakened 3V3 lines, oxidation on sockets,

Sounds like a case of "it's always the PSU" in figurative sense... e.g. half-blown fuses, dried up caps, good +12V but weakened 3V3 lines, oxidation on sockets, things of that nature. Or it could be platform quirks, or more interesting failures like crystal oscillator degrading, but I'd leave those to later.