WHILE SLOWLY BACKING UP WITH TRAILER ATTACHED VEHICLE SUDDENLY ACCELERATED. TRAILER JACK KNIFED AND CRASHED INTO METAL BUILDING. CONSUMER HAD BRAKES APPLIED. THEN, SHIFTED TO DRIVE. VEHICLE ACCELERATED TO 35-40 MPH ,AND HEADED TOWARDS A LAKE. CONSUMER SHUT OFF ENGINE TO STOP VEHICLE. DAMAGE TO VEHICLE WAS $ 5000.00, DAMAGE TO BUILDING UNKNOWN. NO INJURIES. *AK *SLC