Hi
Don't have that game, but would look at the credit unit, even if the "0" switch is closed, the unit I believe shud still advance the credit wheel when coins are dropped. make sure it works manually, and the other switches work.
chk the ball count unit, make sure it goes all the way up/down manually.
if thats not it, maybe game over relay, or maybe tilt relay?
or...maybe start relay? kinda guessing here.