Hi Darren,
I have a power button like that. It is lit up. All leds on the motherboard flash short and then turn when switching the button on the psu. After 20 seconds the rgb memory is also lit up, but no joy when pressing the power button.
It is my 4th build, so I am no newby. CPU is installed correctly by aligning en pressing with lever.
I need to say that when i looked to my 24atx cable on one pin there is a bend edge. Maybe that is causing a problem...
Going to de-assemble my build and test the main board on the cardboard box...
Is there a way to test de psu without the motherboard and cpu?