The playfield is probably remaining dead since the ball gate is not being energized. As soon as the motor completes the game reset, the game-over relay is immediately re-energizing, killing the playfield since the balls are still sitting on the 4th and 5th trough switches, (which is the correct operation).

I'd first check-adjust the 3 switches at the ball trough coil. In adjusting these switches, one of them should be energizing the trough coil as mentioned above. If you didn't experience this, you may have a bad coil. After doing this, I'd be checking the switches on both the SB and DB relays. You'll need to really get a good look at these switches with good light, the machine unplugged, and checking both relays in both energized and de-energized positions.

Unless there's a "Reset-completed" relay, the DB is the relay that keeps the score motor running, turning the score reels to "0" in it's DE-ENERGIZED state, then energizes at the END of the reset, killing the score motor, and game play may begin. This relay lives its life in its energized state, only performing its function when de-energized.