My garage door goes down than back up. how do i fix this? there are no obstructions that i can tell. the sensors seems to be lined up.

check the travel, it may set too much.

There might not be an obstruction, but the opener THINKS there's an obstruction.
Check that there is nothing between the lenses of the two sensors. Even a spider web can trigger the safety.
If there is truly NOTHING obstructing the sensors' view of each other, then you should carefully re-align the sensors.
Also, make sure that all the screws and bolts on the rails are good and tight. As the door is used, bolts can loosen, which makes the rails start to vibrate and rattle during the door's movement. Eventually, all this vibration can make the sensors lose alignment.

Hi. The sensor with the yellow light is telling you that it is miss-aligned, Usually it only takes getting bumped to knock them out of alignment.
I would slowly turn or adjust the positioning of the sensor.
The one with the yellow light should turn green when it is all the way in line so that the beam is completing it's path.

It's out of adjustment, so the sensor is looking at it like there is an object blocking the door from closing.
It's called the obstruction sensor.
It's there as a safety feature, so that the door doesn't come down and smash anything in the opening.

I hope this helps you out.

There is a sensor which checks for obstructions, are you sure there is nothing impeding drive path?Inspect the drive path carefully. If it reaches a part of the drive path which causes it to slip or stick slightly this will tell it not to continue. Also but less likely have you checked that the optical sensor is clean and aligned. Make sure there is nothing blocking the optics.

Clear any obstruction from between the safety sensors. Loose leaves, trash, and dirt on the lens of the sensor itself are all examples of things that can obstruct the sensor's signal.

1. Check each sensor for a steady glowing indicator light. If both indicator lights are on, or if one indicator light is flickering, the sensors may be slightly misaligned. To check for misalignment; obstruct the beam of the sensors so that they cannot see each other. When the beam is blocked, the indicator light on one of the two sensors will temporarily go out. This is the receiving sensor. Remove the obstruction and loosen the wing nut on the back of the receiving sensor. Adjust the receiving sensor until the green indicator light goes out, if not already out, then realign until the green light is bright and steady, then retighten the wing nut. This usually takes a couple of attempts before it is back in alignment.
   

2. If an indicator light is out on one or both sensors, check for a possible loose or shorted wire. Sensor wires are attached to the white and black terminals on the back or side panel of the overhead motor unit. Check that they are securely connected to each terminal. Also check the wires for any breaks, especially anywhere they are spliced together.
   

Remove the chain from the sprocket and then run the motor until the sprocket turns clockwise and stops. With the door in the closed position and everything attached to it, replace the chain and tighten. This will get everything back into sync. You will most likely have to tweak the up and down limits a bit. Do not over tighten the chain. It should sag just a little.

If the door is hitting the floor and then reversing you need to adjust the 'down limit' which is on the side of the motor unit. Turn it a bit in the opposite direction of the arrow printed on the cover. Some tweaking may be necessary.

wayne dalton classic drive squeaks and binds then stops

first try to add some pressure by turning knob on back of operator, if this does not help inspect circuit board look for indication of a burn some times this is just a brown or dark yellow line in board check gear also and look for shavings... gear kits and circuit boards are not cheap yet easy to install.

what brand. you described three sensor lights/ Craftsman/Liftmaster have two, Sounds like saftey beam problem,