My pc will not turn on

My pc will not turn on

The PSU has a green light, but i press the power button and the pc does not turn on. I disconnected a cable from the motherboard that had 2 yellow and 2 black wires and all the fans started spinning, but the pc was not on... It is a 8104Y2B Lenovo IBM thinkcentre. I ordered a graphics card for this pc, so i want to get this pc fixed before it arrives next month (February). All help is greatly appreciated! Thank you in advance.