Won't start a game

I rebuilt all of the flippers. After each one, I tested the game to make sure the flipper was working properly, and things were fine after the first three. But after rebuilding the fourth flipper, it wouldn't start a game. The lights come on, and if I flick the mechanism on the inside of the coin door as if I were adding money to the machine, the I can hear reels spinning inside the cabinet, but it just won't start a game. As far as I can tell, the game has six fuses (four near the transformer, and two on the underside of the playfield, and they all test fine. I did replace the flipper buttons and the start button on Monday night, but I'm pretty confident that it's not a problem with the start button because it's properly closing the leaf switch. I'm sure it's probably something simple, but I'm not sure what the issue is.