I pulled all the disk and tried to start it. It will not start if any of the backplanes are connected. Are all 5 backplanes independent or are they connected somehow? I also tested with cables that are know to work (used the one to power the fan assembly). I also tested with the hdd controller cards pulled. It is always when the backplanes are plugged in that the fans and computer will not start up.
If the back-planes can be independently plugged in, find out which is preventing the power supply from starting. (disconnect all but one at a time)
Then, once you know which, If the back-planes can be dis-assembled, you might try removing each in turn looking for stray pieces of metal/wire/screws/hardware/washers, etc. That's all it would take to short out a power bus. It is possible that vibration caused something to vibrate/move to where it would short out the back of the back-plane. (or equally possible a stray two-year-old decided the slots on the top of the server looked exactly like those on their piggy-bank, and started feeding in pennies...