Z270M Pro 4 won't boot

Thanks for your answer. Im going to try that but I won't be able to test the CPU as I don't have any recent other motherboard.

I've tried everything I could. I did a last clear cmos with the method you provided me. I tried another PSU. I've checked pci express slots in case something was stuck in there. I've checked 2 times CPU and socket. I re built it starting from zero. And still a black screen. That's crazy all I did was switching my graphic card to another pci express slot like I did several times before. Now I don't know if it's a CPU issue or a motherboard one.

I really did not understand what the entire situation was just from the first post, but now I do.

Given all the things you said you tried, something obviously broke. Since you have the board out of the case, check the bottom of the board, particularly the PCIe slot solder points. Or possibly a small component on the board's top was damaged or broken off when moving the video card from slot to slot. Or possibly a static electricity discharge zapped something on the board. Or the hot environment inside the PC case from the video card caused a part on the board to fail.

Since you cannot even get the Intel iGPU to produce a signal to the monitor, and tried a different PSU, unless your memory suddenly died, about all that is left is the board has a problem. Was the video card removed from the PC when you tried to use the Intel iGPU? That would be important to do, since you could not get into the UEFI/BIOS to enable both video sources. Clearing the CMOS after removing the video card and trying the iGPU might help it work.

Besides testing the video card in another board, not much else left to do.