Right - sounds good mate.. No credits..
Two ways to look at this. This is basically a Williams Machine, and they can have a problem whereby the coin switch arm gets caught at the bottom of it's travel. So check in your coin door to see if they both moving freely. Check that the contacts are making contact, and then try to give the game some credits...
Other way is to turn the game off, and advance the "Credit" wheel by moving the plunger...
Switch the game on, press the start button..
Report back when done !