For my money, you've got a bum power supply. Thomas is right about the LED brightness thing, believe him.
You could try taking apart the power supply (if you don't value your life much) and look on the underside of the pcb for the p/s. I have repaired a couple where there were lead solder traces that had deteriorated over time ending up with a machine with symptoms like yours. I suspect the p/s most of all because you say the machine was working before you put it in the closet. You should also make sure that the power supply connector on the bottom of the m/b is not grounding to the case (this causes all kinds of whacko problems). A little extra plastic in this area is a good idea. A dead but recently moved machine can also be symptomatic of a bad cpu card contact. Those little pins on the cpu slot can drift over time so the cpu card doesn't make good contact. Just my five cents worth......
