I have a Craftsman 1/2HP garage door opener that won't close with out holding the button inside the garage. If you use the remote or push the button and let it go, it moves about 2 inches and the returns to open. The limit sensors are all OK and both of the eye sensors have a solid green light on them. If you hold the button in the garage, the door will shut all the way. It will then open fine, but return to the same issue of not closing. I have tried blocking the sensors to see of the green lights ever change and they never do. They just stay solid green all the time. Have the sensors gone bad? Please help.