Z axis not performing

all of a sudden the z axcis does not resspond as it should will getvto about 15mm deep with now problem , then it does not rise to clear the work but plws straight across the work and then burries it self , now when if setting up if i jog it up once o’k second jog and it comes down in stead of going up thismachine is now 3 years old have had no problems apart from the humane factor the controller has not been upgraded any sujestions anyone i am in new zealand

Check the set screws that hold the pulley onto the Acme screw.
Many reports of them coming loose and even vanishing.

Hello Mark the screws are tight the acme is all o’k it apears to be in the controller

Check and double check that all four wires for Z-stepper are intact, no loose contacts.
If one of the four wires have no contact the stepper will operate as usual but directional control is lost (Random direction, usually in the direction of least resistance)

All contacts are tight

And do the wires conduct? (Measure resistance or use the diode tester found on most DVM´s)