Question Motherboard on new build shows no sign of life ?

[Homilica]

Need help!

im kinda stumped and feel that im tired and overthinking.
Brand new build:

Mobo: Asus Tuf X670E
CPU: Ryzen 7800X
GPU: RTX 4090
PSU: Corsair RM1000x

Problem is once the PSU is switched on mobo shows no life. not even the standby by backlit LEDs. I can force the PSU on by disconnecting MOBO and shorting pins 3 and 4 and then everything works, all fans. all lights. the screen on the water cooler etc.

So thinking it was a DOA mobo i swapped it with same model and same results/ thinking maybe PSU or the power cable (from wall or the main 24pin) was faulty. swapped all cables and the PSU (another rm1000x) same results. no life.... tried with no cpu installed. tried with no ram installed, tried with no gpu installed or anything but power cables and nothing, still no lights on mobo ?

 

[dvinell]

Are all the power connectors to the motherboard connected properly?

 

[Homilica]

Are all the power connectors to the motherboard connected properly?

Yes they are.

 

[dvinell]

That is confusing.
Two motherboards and two power supplies not powering up?
What happens if you short the "power switch" jumper on the mobo and bypass the case switch?