Try taking a hair dryer and warm up the motherboard and try powering up the control, if this doesn't work try warming up other part's in the electrical cabinet until you find the spot that let's the control start up.
Once you have found the area that needs to be warmed up in order for the control to fire up, take a closer look at all the capacitors on that circuit board, after yrs the capacitors begin to dry out and don't take the cold so well.
I have resolered capacitors on old fanuc controls that would on fire up if heated with a hair dryer, these same control's ran like new afterwards.
