Door will not open at all, usually a broken spring - the opener is not strong enough to lift the full weight alone. Opened partway and jammed, often a cable off its drum or an obstruction in the track. Came off its tracks entirely after an impact or a broken roller, do not force it further in either direction.
One side hanging lower than the other points to a cable or a spring that failed on just that side - the door is still under uneven tension and should not be cycled. Opener runs but the door itself does not move is almost always a stripped gear inside the opener or a broken spring, not a dead opener - replacing the opener would not fix either one.
Door reverses the instant it starts closing is usually the safety sensors near the floor, misaligned or with something blocking the beam between them - a five-minute realignment that people still pay a call-out fee for, and one we will not pad into a bigger repair if that is genuinely all it is.
