PSU with a model number HP-D2402E0

PSU with a model number HP-D2402E0

Fault: When the start button on the desktop is pressed the fan briefly (1 or 2 seconds) starts spinning and then stops. Sometimes it will continue starting and stopping, other times it will cycle once and then stop.

Tests conducted: I removed the PSU from the desktop case and plugged it in to the mains. I then shorted the green wire to earth and the fan spun up normaly So when the PSU is connected to the motherboard it fails but when it is disconnected from the motherboard it works as normal.

Posible conclusion: From what I can see I think it may be the motherboard.

Any thoughts on the subject would be appreciated.

Maybe a load on PSU rails is required to cause fault to show up in PSU. It may also be the MB. Try any pus that will fit and see if it has the same problem. Look for swollen caps everywhere.