Desktop PC, complete loss of power. Good (new) PSU, and new Motherboard.

Complete lack of power to desktop PC - My story: I built a gaming PC which has been working without any issues for about 3 years. One morning, it would not boot. No fans, lights, beeps, ect.. as if it was unplugged. (it's not. I checked, multiple times as i figured i must be going crazy)

I immediately thought of the PSU and MB. bought a brand new PSU, same wattage, nothing.

Bought a replacement motherboard, same model, still nothing.

I can't get it to post, i can't even get a fan running. It's acting as if it's completely unplugged.

Things i've tried: PSU in another computer, works great! (both old and new PSU). Tried old and new MB out of case to eliminate grounding issue. disconnected hard drive, GPU, and even CPU to see if i could get ANY errors or signs of life. Tested PSU with voltage meter.

Could a bad CPU or bad Ram cause a complete loss of power? Or is there any other way to tell what it might be? I figured if it was any other component, CPU, hard Drive, ect... I should at least get POST or some sign of life... you all are my only hope before buying something pre-built because i cannot figure out what could be causing this... Thank you for any ideas or theories!

Motherboard: ASRock 370 Pro4

CPU: Ryzen 7 Processor,

PSU: 650 watt P

GPU: Geforce GTX 1660 TI