First thing to test is the voltage at your wall socket.
115V minimum needed for most games--but for 4-flipper games like STTNG: 117V minimum.
How-to is shown in the below link in 4.8.3.
If that's not it, you'll have to then methodically follow each step in the guide in sequence and rule each one out one-by-one.
The Z-connector is a known trouble spot on that particular game as well...so it never hurts to eliminate it at will.
Lots of helpful responders here to assist.