[ IBM 5160 with IBM 130 watt power supply. ]



So:
* The power supply's fan turns when only the hard drive is attached, and
* The power supply's fan does not turn when only the motherboard P9 (+/- 5 volts) connector is attached.

Both of those loads are known to be sufficient on their own to operate the IBM 130 watt power supply in a 5160.


CONCLUSION:  The 5160 motherboard has a short-circuit in either the +5 or -5 volt rails.


What Now?

It is very highly likely that one of the Tantalum capacitors on the +5 or -5 volt rails of your 5160 motherboard is short-circuit.
Faulty Tantalum capacitors is a very common problem with the 5160 motherboard.

Visually inspecting the Tantalum capacitors may (repeat: may) reveal the faulty capacitor.
In some cases, the faulty Tantalum capacitor may only have a small black eye/hole, as pictured below.



But the faulty Tantalum capacitor may have absolutely no visual indication of failure.