Garage door opener problem

I have a Chamberlain Whisper Drive garage door opener. The sensors are malfunctioning. The one with the yellow light is solid like it should be. But no matter what I do, I can't get the green light to stay lit. At best, there is a barely noticeable flicker that still prevents the door from closing.

The door doesn't move when I use the remotes. When I use the wired controller, the door starts to close but immediately reverses. To close the door, I have to hold the wired button until the door is closed. THis doesn't work with the remotes.

Strange thing is, there has been a few periods, of three or four days, where the door was working fine. Once, it worked with no problems for 3 days, then stopped working. I looked at the sensor and the green light was completely out.