Need help identifying a fault please. Motherboard related.

Hey, my Xbox One stopped working a couple of months back and I gave up trying to fix it after looking online at the common causes. I think the motherboard is damaged somehow, my power supply is working perfect, I have 3 of those so I know it's definitely not the issue.

I was wondering if someone in the community with repair experience on Xbox One consoles could shed some light on where the fault might lie?

I have the console open on my desk, when I plug the power supply in the fan spins briefly for 2-3 seconds and then stops, the fan does this 3 times before giving up completely.

When I attempt to press the power button on the front of the console I get no sound, no ding, nor does the fan spin when I press it. Same applies to the eject button.

I've been fixing tech for a few years now so I'm no rookie, if anything I'm treating this as a project so I'll try anything to get it going again.

Thanks for looking, I really hope someone out there has an idea what this might be.

Kind regards, Jihiro