Doby

Can you try another psu in it first? That would be the best and easiest at this point.

Check the clear cmos jumper is on pins 1&2 and did not come dislodged or something, a board could act like that if the jumper is not on pins 1&2.

I would even replace the jumper cap, I have ran into one were it was not making contact.

If you try a known working psu and all jumpers are on the correct pins I suspect its the motherboard