I've got a 5 year old Optiplex 9020 that is failing to boot. By that, I mean when power is applied to the CPU, the unit appears to be powering up for about 2 secs, beeps once and restarts, repeating over and over. It never gets to the point where the diagnostic LEDs power on or you can run pre-boot diagnostics.

I tried swapping out the power supply from a working 9020 but that had no effect. I tried disconnecting the hard drive and DVD drive but that had no effect either.

Seems likely this is a motherboard issue but I've never had one fail so I'm not familiar with the symptoms for that.

Any suggestions?