I have a Craftsman 139.53982SRT door opener and it

I have a Craftsman 139.53982SRT door opener and it stopped working all together. The light on the control console on the wall is not lit. Once in a while it will light up and it works, but mostly the light is out and doesn't work. If I go up to the motor unit and tap on it the light comes on and it works. It only works for a few minutes. What could this be? All power is running in garage, and no circuits have been tripped.