I had a mono/poly that died on me - turned out the molex connector had worked itself loose from bad solder joints from the PS board ... while i didnt' have your symptoms I could easily see something like this causing that - sounds like you have an intermittent problem somewhere - could be bad fuse contacts, bad ground, lots of things - check your contacts and wiring maybe - then check or reflow your solder joints with the PS out of the enclosure
