Question Motherboard keeps dying ?

Jun 23, 2021
I know enough about pc's to solve some simple issues, however this one is annoying me. My best guess could be that the power supply is at fault.

I recently built my brother a pc, it was a mixture of second hand parts along side new ones. My brother got a few parts (including the PSU) from the used market. However it was labelled as new, although even at that the cpu wasn't new as it had marks on it.

Anyways I built him the pc few weeks ago and after a little while it wouldn't turn on. I did all the trouble shooting steps, eg checked the power switch cable. Ram, all power cables etc. I even jump started the power supply to see if it works and it did indeed work so I just assumed that the motherboard just died. Although it was brand new. Regardless I returned the motherboard and ordered a replacement. After I Installed the replacement, 2 days later the same thing happened. Motherboard is just dead. Any ideas? My best guess is the power supply. I think the power supply is a seasonic one.