The CLUNK is probably a high current contactor for the axis/spindle amplifiers. You could have a problem on a drive, a power supply, or an Estop condition ( axis overtravel etc). Try holding the OT release down and power up. That will eliminate that problem. If its a Yasnac machine, I have had the old drives fail just like you describe. The old capacitors in them dry up and won't charge for a few hours.