It will not open
Six causes cover nearly all of it. They are listed here in the order worth checking, which is to say the free ones first.
Call to get it looked atLicensed New Hampshire technicians1. Ice at the bottom, if it is cold
Between December and March this is the first thing to rule out, because forcing it is what turns a stuck door into a broken one. How to free it properly.
2. The spring
Look for a gap in the spring above the opening, then pull the release cord and try the weight by hand. Heavy means the spring. The full check.
3. The safety sensors
Two small eyes face each other a few inches off the floor. If their beam is broken or they are out of alignment, the door will close a few inches and reverse, or refuse to move at all, usually with a blinking light on the motor unit.
This is the one that most often fixes itself in a minute. A bag leaning against a bracket, a cobweb, road grit on the lens, or a knock that twisted one sensor a few degrees. Wipe both lenses, make sure they point at each other, and look for a steady indicator light on each.
4. Power
Worth two seconds: is the motor unit plugged in, and has the circuit tripped? A freezer or a second fridge sharing the circuit can do it. If the wall button works but the remote does not, that is a remote problem rather than a door problem — usually a flat battery, which the cold brings on early.
5. The trolley is disconnected
If the motor runs normally and the door does not move at all, someone may have pulled the release cord and left it disengaged. The carriage reconnects by pulling the cord back toward the motor, or by running the opener until it re-latches, depending on the model.
6. The opener itself
A motor that hums without turning, or runs with a grinding note and no movement, is usually a stripped drive gear. That is a repair rather than a replacement on most units. More on openers.
When to stop and call
Stop if the door is crooked in the opening, if a cable is hanging loose, if you can see a gap in the spring, or if the door is heavy by hand. Those are load-bearing parts under tension, and the failure modes are not gentle.