Do they fire if you ground them?

When the machine boots up you should here the flipper relay on the driver board (big ugly rectangle thing on the left side of the board between the connectors) engage near the end of the sequence. The cpu controls this through one of the wires in the top left connector of the cpu board I believe. Gently apply pressure against the connector to see if you have a bad connection. The other issue can be you have a bad flipper relay. And as suggested above make sure you have current running to the flippers

Mike V

Cracked solder joints on those connectors are very common. You can have a buddy hold a flipper button in while you gently wiggle the connectors on the board to see if the flippers magically start working again. If so, reflow or replace the solder on the back of those male connector pins. The pins on the female connectors are always suspect, too, especially with Bally/Stern games.