Replace the spring(s). A new set is about 25 dollars yo...

It all depends on what kind of spring it is. There are extension springs that expand and contract as the door opens and closes and run on a series of cables and pulleys. If you have this type, you need to put your door all the way in the up position(have someone help you lift it)and clamp it into place by locking vice grips in the track under the bottom rollers. Now you can take your broken spring down, and take it with you and get the correct length and width for your door at a hardware store or garage door company. Get 2 springs! both will need to be changed since the other is probably ready to break as well!!! Now you can replace the broken one's side first while looking at the good one as a diagram. Then repace the other, and make sure the springs are close to the same tension as this will affect the way your door rolls in the track(it may need some adjustment afterwards). Always think about what you are doing and possible consequences before you start working on any garage door components as a wrong move could leave you missing fingers or worse. If you have long black springs mounted on a long tube above your door DON'T TOUCH ANYTHING!! These are torsion springs and should only be replaced by a professional! You should pay no more than 150.00 to 200.00 for BOTH of these kind of springs to be replaced, call around and find a garage door service company that will guarantee you a good price before they come out! Alot of these guys are huge con artists and will trap you by telling you it will be a 55.00 trip charge plus parts and labor. You can end up spending hundreds even thousands. Oh and don't replace your opener until you fix the springs and see if it still works.

just do the spring, it's cheap.