This typically happens for two reasons. The most common is closing the door on something that was stored in the corners. We always advise to keep objects out of the corners to avoid this. The second reason is the springs are broke or have lost tension, allowing the cable to pop off in the up position. Luckily for this gentlemen here we were able to get this door back on track, but in 16 years this is probably the worst cable off service I have seen. The only thing keeping that door up was two bottom rollers still in the track and the opener arm holding the top section up. This is incredibly dangerous for even an expert and should not be attempted by a homeowner whatsoever. Call the pros who kniw at A Plus Garage Door Service, inc.