You can test the unit without a psu first my just shorting the white ond blue wires coming from your mach, this will run the unit up to boot temp then the unit will shut down
To run the mach off a psu you will need to start the mach by shorting the blue and white wires, but before it reaches boot temp plug the molex connector into a working psu ( ie one you have already jumpered the black and green wires to make the psu run).
Do not plug the psu into the mach if you have not already started the mach by shorting the blue and white wires, the mach will run but it is an easy way to corrupt the machs firmware