Alex,

Failed switch or wiring. Need to check mast prox switch inside battery compartment. Make sure all wiring is still in tact. Also, the foot switch could have failed. Make sure the brake release switch is spring loaded. Failed springs allow the switch to constantly make contact. You also have a prox switch for the steer motor. Make sure all the wiring and sensor is still in good condition. Some lifts have safety arms that must be in the down position for the lift to start. Could also be other issues with electrical or fuses. Good Luck.