Springs typically only have a certain amount of cycles before they break. A cycle is considered once up and once down.
The symptoms typically include the opener runs but does not lift the door, or inside the opener the customer may have white shavings from the gear. This is a common winter problem if the door freezes to the floor. Can also happen when door is run with broken springs. Any Liftmaster, Chamberlain, Sears Craftsman may have this problem.