PC will not power on, can't figure out why.

Hi team, having an issue with my PC and can't figure out the culprit.

I was using the PC fine last night, haven't had any issues for some time. Before I went to bed windows had an update ready so I clicked update and shut down then went to bed.

Woke up this morning, pressed the power on button and nothing is happening. Not even a brief spin up of the fans. The backlight on my keyboard does light up so there's power to the IO at least, but I can't see any other lights on the mobo or any signs of life.

I've tried unplugging and holding the power button down for a minute. I've reseated the front panel pin connectors. I've tried shorting the power pins. I've taken the CMOS battery out for five minutes and tried again. I've unplugged every cable on the motherboard and reseated them. I've swapped the RAM in the slots.

No change, no lights anywhere on the motherboard and no fans spinning up. The only indicator that it's not a brick is the backlight on the keyboard.

Going to try unplugging motherboard cables and redoing them just in case, but that's the last thing I can think to try that doesn't involve replacing parts.

Any ideas for forcing this thing to turn on?

All parts were bought new in November 2022 so the PC is barely two years old.