Did you get the manuals with the machine? If all else fails, If you have the PMC ladder listing and can display it and can find the Z homing routine, you can usually trace the reason for the hold up in the zero routine, the highlighted objects show the parts of the path that are completed.
It could be something to do with the spindle orientation, although of course you need it to tool change, it is seldom programmed in to enable zero.
Al.
CNC, Mechatronics Integration and Custom Machine Design
“Logic will get you from A to B. Imagination will take you everywhere.”
Albert E.