Its plugged in to the mother board but when I power on the psu nothing happens. But If I press the mother board power on button (only if psu 'on') I hear a click in the psu. is the psu faulty or am I just doing something wrong? I have asrock z87 extreme4 and I have connected the 20+4 pin to mono and the 4+4 pin. And I have conneced 6+2 pins(2) to gpu. And my hdd is connected.
What you're doing is simulating the motherboard sending the PS_ON# or Power On signal to the PSU. The motherboard will only send out this signal to the PSU if it has determined that all of the PSU's voltages are within ATX12V specs.
Since the motherboard isn't sending this PS_ON# or Power On signal to the PSU then there must be a problem with the PSU.
Borrow and try a different/better PSU to troubleshoot with.