I couple things to try besides checking fuses or circuit breakers etc.
Push the Z axis about a foot or so towards the chuck when the machine is off.
Boot the control and home the machine. If the Z moves, then manually trigger the homing switch early. If the machine homes there, it may be a simple adjustment of the switch or cam.
If the Z does not move, then either there is an issue with the servo amp or motor. During the homing cycle, monitor the LED indicators on the servo amps. See if something is different between the two amps before and after homing.
You can swap the cables and connections between servo amps to see if the problem moves to the other axis. I'm not a big fan of swapping axis motors, but if they are the same, it is a last ditch option.
Some machines had a utility on the hard drive that allows I/O diagnostics. I cannot recall the name off hand. EZSPS or something along that line.
Short of that;
Someone qualified, could check that the homing switch is getting to the control AUF card JP14-1B or JP14-2B. I don't think there was an LED indicator, so it may need verified with a multimeter while someone else is triggering the switch.
If all is well with the home switch, next check the encoder signals at the AXZBOB card JP4. This will be done with the machine on, but not homed yet. Best to use a logic probe or O-scope as the Z screw is rotated by hand.
JP-4 pin x =
1=A-
2=A+
3=B-
4=B+
8=Z+
9=Z-
6=+5v
5=0v
7=0v shield
10=0v shield
Calling in a good local tech would be less risky than attempting this on your own, if beyond your experience. Just don't create more problems than you really know how to solve!
DC