CAR IN PARK , IGNITION OFF. ENTERED CAR AND STARTED TO MOVE CAR APPROXIMATELY 30-25' TO PARK IN FRONT OF GARAGE. STEEL GARAGE DOOR DOWN. PROCEEDED TO GARAGE DOOR 1-2 MPH WITH FOOT ON BREAK. CAR ACCELERATED AT HIGH SPEED AND COULD NOT STOP OR SLOW DOWN CAR AND IT CRASHED THROUGH GARAGE DOOR AND WAS STOPED BY BOXES AT BACK OF GARAGE. ACCELERATION SUDDEN AND HIGH WITH NO INDICATION OF WHY. CAR DAMAGED DUE TO DEBRIS FROM FRAGMENTS OF STEEL DOOR MOSTLY ON TOP AND FRONT AND DRIVER SIDE OF CAR. AIRBAG DID NOT DEPLOY. CAR IN MY DRIVEWAY AT TIME OF ACCIDENT. MECHANIC UNABLE TO DETERMINE CAUSE. RECORDS AVAILABLE.