The door closes then immediately reopens
This is the safety reversing system, nearly every time. Check the two photo eyes near the floor on each side. One should show a steady light. If it is off or blinking, the eyes are misaligned or something is in the beam. Wipe the lenses and adjust the brackets until both lights are steady.
The motor hums but nothing moves
On a chain or belt opener this usually means a stripped drive gear inside the head, which is a common and repairable failure. On some models it is a failed capacitor. Either way it is typically much cheaper than a whole new opener.
Nothing at all happens
Check the obvious: the outlet has power, the opener is plugged in, and the wall button works. If the wall button works and the remotes do not, the problem is the remotes or the receiver, not the motor.
Only one remote works
Replace the battery in the dead one first. If that fails, re-program it. Most openers pair by pressing the Learn button on the motor head and then the remote button within thirty seconds.
The door stops partway or does not close fully
Travel limits drift over time, especially after a season of temperature swings. Most units have up and down limit adjustments on the motor housing. Adjust in small increments and test.
The door reverses before it touches the floor
Either the close-force setting is too low, or the door itself has gone out of balance and is harder to move than the opener expects. Test the balance by hand before touching the force screw; turning up the force on an unbalanced door hides a real problem.
When to hand it over
If any of this points at springs, cables or a door that has gone out of balance, that is the point to stop. Supreme Garage Doors Repair Services covers garage door opener repair and every other garage door service across New Hampshire, with same-day slots most days and a line answered 24 hours at (888) 904-6236.