Question PC power button isn't working

[Ray Plays]

Hey! My friend bought a computer today (i7-2600k, 16Gb ddr3, XFX radeon RX570 8gb, 550W psu) and a brand new case. We pick everything out from the old case and putted in the new one. When we plugged in the pc and pressed the power button, nothing happened... then we checked the front panel connection, every cable is connectes correctly, we plugged in a mouse to check the voltage in the mobo, the mouse led is glowed... then when I tried to plug out the psu main cable from the mobo (without switching off the psu) and then plug in again ,the pc started automatically... then in the windows we shutdown the pc and tried to turn it on with the power button but again nothing happened..
Where is the problem? :/

 

[Ray Plays]

Also tried to turn it on without the gpu, but nothing