Try it outside the case with bare minimum parts? Sometimes I find the build has shorted out the board in the case or forgot to check jumpers. A few boards won't power up with the CMOS jumper in its reset position.
Not really a "help me fix it thread" but I wanted to ask a question about a motherboard I was working with lately, a friend built himself a pc with a Ryzen 5 2600, 2x4GB DDR4 vengeance LPX ram, a corsair VS550 and a Tomahawk B450 board. Once he tried starting it, nothing turned on, basically zero reaction. He checked for any problems on the motherboard itself then called me, we tried replacing everything, the psu, the ram and the cpu itself, still zero reaction and we tried 3 working PSUs. So with zero visible damage to the board and every other component working what could have been causing the no power problem? I told him to return the board on warranty and he did by now.