Won't stay on. Power loops on and off for 2 seconds indefinintly.

As soon as I hit the power button, the fan turns on, buttons light up, and I see the desktop screen. Then it shuts down and tries to turn on again. I timed it and it is just under 2 seconds that it stays on. Off for less than a second. I have to hold the power button to stop the loop.

Does a part need to be replaced?

It was working 2-days ago. I checked all the connections. Nothing was disconnected but I still disconnected and reconnected cause why not.

Anyways, long ramble over. Any advice is most appreciated.