There are many times you back out the driveway, push the remote control and the garage door doesn’t close. One of the issues could be the safety sensors. The Liftmaster safety beams are a bit tricky at times; they can fool you into thinking they are working correctly. It's best to have it dark in the garage by closing the garage door. With the garage door closed go to the safety sensor with the green light and look at it for 3-4 seconds, you may have to get down closer to the sensor to see if the green light is flickering, pulsating or lightly flashing. If so, you will need to adjust the safety sensor by loosening the butterfly nut and move the sensor, referring to the white arrow in the image, align that edge parallel with the garage door. The objective is to align the sensor with the other sensor (amber light, the sending sensor) so the two can talk to each other. Image a 5 inch diameter tube from one sensor to the other, If the infrared light is shooting across the front of the garage and it is barely outside the 5 inch imaginary tube, the green light will flicker, pulsate, or flash so lightly you will think the safety system is working correctly. You should know if the amber light sensor is not aligned, the green light sensor will be doing the flashing, even though it is correctly aligned. We are assuming the safety sensors worked correctly at one time or another and this issue only just started. If so, there is one other issue that could be the problem, the wires themselves could be shorting out, in which case I have found it is best to change all the wires running from the safety sensors to the head unit. The amount of hours spent to find a short in a wire is very time consuming. Changing all the wiring will solve any issues. If the safety sensors still refuse to work correctly then the bad news is the logic board shorted out and needs to be replaced. Hope this helps, the first two issues most home owners can probably do themselves, the third issue will require a technician to repair.