the pinscore displays have a test button. When you push it what happens? If all power is good they will run through their self test sequence eliminating it as a source of trouble.

Can you use a DMM? If so what does your power supply read at the test points? If your ribbon cable is bad it will cause all sorts of funny things but until your display does the self test its looking like a power issue.

You have power supply issues for sure or problem with wiring or connectors. Test power supply voltages first. As for getting readings, set to dc volts and ground the black lead to cabinet ground strap and test the power supply at the test points. pinwiki has pictures and procedures for you.
Report back your voltages.
should be an easy fix.