Well, I got a headscratcher. On a unit I built for a friend, twice in two weeks it suddenly locked. The monitor goes black, and the system speaker emits a slow, regular monotone series of beeps. Okay, now is where it gets wierd: All the fans and lights in the box are on but the system is locked; if restart and the power buttons are pressed, nothing happens. The only way to stop the unit is to unplug the power cord from the surge protector! If I wait a few seconds, re-plug in the power cord and press the power button it fires up and runs like all is well. It runs absolutely perfect, with no crashes, error messages or blue screens at any time. It is consistently running 118-120 Fahrenheit, so it's not overheating. Okay, I replaced the power supply with one of my own that has been working perfectly for a year, and it's 400Watts so there's no power starvation. It just now did the same thing, this time twice on one day. Now even the vent fans power off. Still have to pull the power plug to get it to shut down. If anyone has any suggestions as to the cause, I would appreciate your thought.

It sounds like you have an interrmitteny short in one of the units. The power supply seems to be shutting down. It takes a while to reset itself before it will power up again. That's a very difficult problem to diagnose. Uou might want to consider taking it to a shop where they can swap things in and outt.