I have a Craftsman 1/2 hp GDO. It suddenly will not open or close. When I try to open it from the remote or the pad inside the house, it behaves the same way. I hear a click on every alternate attempt, i.e. it clicks one time and on the next try there is no sound...the attempt after that again produces a click. The door does not move but the light bulb does light up. This opener is about 18 years old. What are the possible causes of this problem?

Thanks for your help.

Sue.