Hp a6720y fans spin no power


Oct 21, 2011
I'm trying to repair an HP a6720y desktop that had overheated. Both the inside of the case and the cpu heat sink were full of dust. The motherboard, an M2N78-LA, had several swollen and leaking caps.
After cleaning it out, the system would not power on. The green light on the power supply came on when the cord was plugged in. When the power button was pushed, the system, cpu and power supply fans would turn briefly then stop.
No bios messages.
I replaced the cpu and motherboard, same symptoms. Unplugged hard drive and dvd power, no help.
I suppose I could have a bad power supply, but the voltages look ok with a meter.

Any other suggestions before I try a new power supply?
Do a bench test of the board out of the case with just the cpu/heatsink, one stick of ram, and onboard video and keyboard connected. Those boards are pretty old; the replacement board may also be bad. The final test is to do a fresh install of windows. If the board is bad, windows won't finish the installation.