MY PC won't boot up and it's power button is a constant yellow light.

[RODDAL]

When I press the power button on my computer it powers up, but the power button light stays a constant yellow instead of the normal blue. The computer also sort of vibrates quietly. I've been told this could a failure of the motherboard or power supply, but I'm not sure.

 

[Lutfij]

1| Due to immense number of SKU's parts and build as well as prebuilt system's around, we'll need you to pass on your full system;s specs or at least the SKU of your system to help us narrow down the components and a possible culprit.
2| How old is your system?
3| If you're under warranty period it'd be best to contact your seller before having us suggest that you should open the side panel and inspect for a culprit.

What was the last thing you were doing prior to this issue? A system that vibrates quietly can indicate a case fan or a PSU fan or the HDD. System's like the Dell OptiPlex have a couple of fail safe options built in which can indicate a faulty component.