Classic series (1550, 2550, 3000) - Power down, put on reset jumper, power up with AC, wait 30 seconds, then remover jumper. System should be back to factory (all zone lights lit)
Power series (1555, 5010) - Power down, connect a jumper from PGM 1 to zone 1, power up with AC, wait 30 seconds or until Zone 1 lights on the keypad, then remove connections and proceed.
Try using one of the two above methods and then listen for the clicking.