You say that the power button lights up? that tells you that power must be reaching the switch, if I understand you correctly.
if the power sw light is coming on, then it implies that the sw is OK
as the wiring would be such that the light is connected AFTER the switch
otherwise the power light would be on as long as a power cord was plugged in

I am inclined towards Morgan, and would ask / suggest that if you have access to another PC or Mo/Bo that you play part swap to find what, exactly, is not playing fair ........