We just had the same problem this morning (cold weather can mess these things up). Not sure what you mean by "not working". Ours would open part-way and then stop (or close part-way and then stop), but could open/close all the way if we held the button on the wall down the entire time it was lifting. After much research online
, we ended up checking the sensors at the bottom of the garage door tracks to make sure that the green light was solid (not flashing). Ours flashed a bit, so we cleaned the "eye" and tightened it in place. Once the green was solid, we thought we were done, but still had the problem.
Then we began adjusting the screws on the unit itself that show pictures of the door opening and closing. We thought we were adjusting the torque in the unit (because we read online
that cold weather can make it more difficult for the motor to work), but in reality we were adjusting the opening and closing "distance". Apparently cold weather can also do something to the tracks, which can require adjustments to be made. Something to do with ground swelling...
Anyway, we also discovered that when we had closed the door manually (red pull-cord) the night before for lack of a better solution, it never properly locked back into position, which was adding to the problem.
So, first, try cleaning the sensors. You need a solid green light for them to function properly. Second, if you have used the manual cord, make sure the arm that it attaches to is locked back into position. You can accomplish this by pulling the manual cord, manually closing the garage, and then pushing the button on the wall. The door arm should lock into place. Third, try using a screwdriver to adjust the open/close distance. Start with a 1/4 turn for each position, and play with it until you find the right setting.
If these suggestions don't address your problem, this link worked for us...http://forum.doityourself.com/doors-windows/368278-garage-door-wont-go-down-cold-weather.html