Most games will have a few switches that cut power to the playing/scoring circuits once the game is over. Here is an example from Bally Safari which may be similar to your game:
Safari power rail (resized).jpg
The switches in red all need to be closed for the playing and scoring features to work.

You'll need to sort out any mechanical issues like this for the game to be reliable. If it doesn't work reliably with the game unplugged and activating it manually it probably needs to be cleaned, worn parts replaced, etc.

/Mark