A door that reverses halfway up, or won't lift past a few inches, is almost always a spring that's lost tension - one side of the shaft is still doing its job and the other isn't. A loud bang followed by a door that won't move at all is usually a snapped spring, and it's safe to leave closed until we get there. Grinding or a wandering roller means the track's out of alignment, often from a bent bracket rather than the track itself. A door that closes, then immediately reopens a few inches, usually means the photo-eye sensors are misaligned or the close-force setting on the opener has drifted - common after a cold snap shifts the frame slightly. If the opener motor runs but the door doesn't move, check the emergency release cord isn't engaged before you call; that one's free to fix yourself.