If the Z-axis is no longer working.

disconnect the power cable to the printer and open the bottom and on the mother board switch the cable to Z-step motor with the one to the extruder step-motor.

close the bottom and start the printer in setting mode.

request the extruder to move forward a little, and if the Z-motor move, you can confirm the Z-motor is working as expected.

You can order a new driver online.

I choose a DM556, because it is cheaper than the DM542.