HP Pavilion a767c

Hoping somebody can shed some light into this tunnel I've crawled into....my sister's HP Pavilion a767c stopped working after a power failure. I bought a new PSU and installed it...still nothing. I disassembled the entire computer and added things back one by one...still nothing. The PSU light blinks green upon being plugged into the board. All components, memory, video card, etc. work in other comptuers, so I narrowed it down to the board. Bought a new one. Same thing. Both PSUs that I've tested blink green upon being plugged into the board. I bench tested both boards with good memory, video card, mouse, keyboard, etc. I'm lost. Could it be the CPU? I don't have another system that will accept that size CPU to test it in. Am I doing something wrong?

What about your hard drive ?

The hdd has nothing to do with the troubleshooting youre currently doing. When testing the motherboards on an older system like yours, the only things you truly need connected are the power, power button, and pc speaker. If the motherboard turns on with no cpu, video or memory detected it should give some sort of audible alert telling you there is an issue with the CPU. Adding your CPU should give the audible alert for memory. Adding memory should give you an audible alert reporting no video adapter. Adding the video adapter should allow the system to POST. However since you have replaced everything except the CPU, that would be the most likely candidate.

EDIT: I meant to also let you know you should look up the beep codes for your system. I know offhand that "no video" is likely going to be one-long beep followed by 2 short ones. If you get no response with the bare minimum plugged in the board is likely shot.

Did you plug in the 4-pin power connector?