yes chewingyu, it sounds like the lift has a lock solenoid on the hydraulic control valve. It works with the operator presence system (the seat switch), when there is a presence in the seat it will unlock the system so it will work. More safety stuff the mfg thought was a good idea ;o). You could check the seat switch and see if there is a problem with it and/or the seatbelt (sometimes the seatbelt works with the seat switch in some models). If everything is ok there then it's more than likely the lock solenoid circuit.