I think its the power supply, since it was giving -5v Power supply errors previously, I check the multi meter values comes as 0. plus green LED not working as well.
Check pair of cables X807. They are uses to send power on signal to power supply. If contact is missed, power supply don't power on.
You can short that contacts (with jumper) on power supply for test. If green LED has turned on - problem in this cables.