I was away for the weekend only to come home to a garage door that had somehow got opened by itself. When I tried to close it, it wouldn't work. The lights come just like normal and if I stand in front of the safety sensors, the lights flash, but the door doesn't close--it doesn't make any noise either. It responds to the remote and the wall circuits just like normal, but no motor action. The unit is only 3 years old so could the motor be bad? Could the door have been opened by from another remote? If so, why doesn't the thing work now?