The most likely problem is something binding the garage door or the lift assemblies but if that is okay then it may be an issue with the worm gear/sprocket assembly in the opener itself.
The link below has more information on how to test the door and should help you pin-point the problem area. The number you provided did not work as a valid number, but if you get the model number off the opener that starts in a "139" then you can use it and the information in the links to find your manual online as well for more details.