Several things could have happened, but the most common after hearing a loud bang would be a broken spring. Take a look at your springs to see if they are intact. If you have extension springs (they would run along the horizontal pieces of door track), make sure both springs are still there and are not broken. If you have safety cables, the spring may be dangling but held up by the cable. If you have a torsion spring (in the header above the door opening), look to see if there are any breaks in the coils. We don’t recommend using your door with a broken spring to avoid injury and avoid more damage to the door system. Call us at 1-800-734-1401 to schedule a repair service or purchase the parts if you prefer to do it yourself.