The first step would be to figure out what is making the score motor run. The switches in the long red box show you which relays can cause the score motor to run:
Sing Along ball return relay (resized).jpg
How many of those relays are active when the game is stuck in reset?

One possibility is that the game has finished resetting, but isn't able to kick the ball to the shooter lane to start the game. The O/Ball Return relay fires when the ball drains and the Outhole switch closes. When the O relay fires, it causes the score motor to turn, and should cause the Ball Return Kicker to fire. If your O relay is active while the score motor is turning, check the two switches in the smaller red boxes. They both need to close to fire the Ball Return Kicker.

/Mark