The machine which I was going to put into my MAME cabinet died last night. It won't boot; it gets partway through the POST routines and freezes. Fortunately, the motherboard has a series of LEDs that indicate where the trouble lies. Unfortunately, it indicates a different problem every time I try to boot it.
After some research, it turns out that the motherboard (a Microstar K7T Pro2) is prone to developing problems with the voltage regulator — problems which can cause the very behavior I'm experiencing.
So... replace it with the cheapest motherboard I can get my hands on, or do the usual upgrade-and-trickle-down?