It could be just the simple problem of the trigger not working. Disconnect the trigger wires from the machine at the plug at the front of the machine. See if you can manually trigger the machine by placing a piece of bent over mig wire onto the contacts. If the machine does trigger from this then your fault is in the torch somewhere. It could be the trigger (which commonly does fault from a dusty environment) which is easily replaced by going into any welding store with the torch model number (magnum 250L), or it could possibly be that a trigger wire has broken from the torch being damaged