A surprising number of the openers we are asked to replace do not need replacing. Before you spend money on a new unit, work through this in order.
The door does not move at all and the motor is silent
Check power first: the outlet, the breaker, and whether the opener is actually plugged in, because they get knocked out more often than you would think. Then check the wall button, which fails more often than the motor does. If the wall button works and the remotes do not, it is a remote or receiver problem, not a motor problem.
The motor hums but nothing moves
Two likely causes. Either the drive gear has stripped, which is a cheap plastic part inside the motor housing, or a spring has broken and the opener physically cannot lift the door. Pull the emergency release and lift the door by hand. If it is impossibly heavy, the problem is the spring, not the opener.
The door starts down then reverses
This is nearly always the photo-eye safety sensors. Look at the small units either side of the door about six inches off the floor. One should show a steady light; if it is blinking or dark, the sensors are misaligned, dirty, or the beam is blocked. Wipe the lenses and adjust until both lights are steady. If that does not fix it, the close-force setting may be too low, or something in the track is obstructing the door.
The door reverses immediately on closing
Usually the down-limit switch is set too low, so the opener thinks it has hit something when it reaches the floor. Adjustable on the motor housing.
The remote only works up close
Batteries first. Then interference: LED bulbs in the opener itself are a very common cause, along with Wi-Fi extenders and some smart bulbs. Swap to an opener-rated LED or a plain incandescent and try again. If range is still poor, the receiver antenna may be damaged or the logic board is failing.
The lights blink a set number of times
That is a diagnostic code. Most manufacturers list them in the manual and on the motor label. On LiftMaster and Chamberlain units, repeated blinking during a close attempt is almost always a sensor fault.
The opener runs but the door only moves a few inches
Force settings, a binding track, or a broken spring. Do not simply crank up the force to power through an obstruction, that is how sections get bent.
When replacement genuinely is the answer
Replace rather than repair if the unit predates 1993 and has no photo-eye sensors, if the logic board and the gear set have both failed, if the chassis or rail is bent, or if the security system is old fixed-code rather than rolling-code. Otherwise opener repair is usually the better value.
If you do replace, a belt drive or a wall-mount jackshaft opener with battery backup is worth the difference in a Maryland storm season.