MEG Z490 ACE won't turn on

[Windowsquasar]

I was in the process of building a PC with an MSI MEG Z490 ACE ATX and after I assembled the PC it would not start. When the PSU (Gigabyte P750GM) is switched on, the start and reset button lights on the mainboard light up. When you turn on the PC, you hear a click in the PSU and nothing happens. Even if nothing is connected, the same thing happens. Without a CPU, GPU, boot drive, etc., the mainboard should at least return an error message, right? The PSU works and I've already tried it with another one. There is also no voltage at the test points on the mainboard. I've also sent the motherboard back twice thinking it was broken.
I've also tried flashing a new BIOS and clearing CMOS.
My final question is: The mainboard itself should do something when it is switched on, even if no CPU, GPU, boot drive, etc is installed? And how do I achieve that?

Thank you for your help.

[Windowsquasar]

It also shows no POST code.

[Savage2k]

On 5/25/2022 at 8:15 AM, Windowsquasar said:

Without a CPU, GPU, boot drive, etc

try to turn on only with 24 pin connected , test 3.3v dram voltage controller and 5v on usb. then plug 8 pin and check 12v rail