My garage door opened fine ... when i went to shut it. i get a 3 sec humm from the unit and nothing else

If you haven't gotten your issue fixed yet... I had the same problem (stopped opening half way when using the remote, went down fine, could lift/close manually fine as well) and this happened on our first cold weather day of the year which was very telling. Anyhow, there are two gauges/dials on your garage door opener unit itself (above, where the light is) which controls how much torque/strength your door uses to open or shut through resistance. I turned mine up some and it now works fine; what likely happened was that the metal tracks or the wood frame condensed in the cold and was providing just enough resistance to stop it when opening - as they have a security device built in to stop if they meet any resistance. Hopefully this helps!

Your trolley may be jammed against the bolt just in front of the motor unit. If so, loosen the chain enough to relieve the strain on the chain and then run the opener until the door is closed. While the door is closed locate the 'up limit' control on the side of the motor unit. Turn this control 2 full turns in the opposite direction of the arrow printed on the cover. Tighten the chain.

2 possible solutions; #1) unplug the motor for 3 mins then replug (resets memory) #2) on back of motor is a "learn button" - press learn button for 3 sec, then press your remotes for 3 sec.

Remove the cover from the motor unit and check the drive gear. It is a white nylon gear just in front of the motor. Also check the door springs. One of them could be broken.

Sounds like maybe the door traveled too far and the trolley has jammed against the bolt just in front of the motor. If so, loosen the chain enough to take the tension off the chain and then run the opener until the door closes. While the door is closed locate the 'up limit' control on the side of the motor unit and turn it 2 full turns in the opposite direction of the arrow printed on the cover. Tighten the chain.

5 flashes is the code for "RPM sensor board or motor overload." If your door is stuck in the open position the trolley may be jammed against a bolt just in front of the motor unit. Remove the bolt and run the opener until the door is closed. Now locate the 'up limit' control on the side of the motor unit and turn it a couple turns in the opposite direction of the arrow printed on the cover. Be sure to replace the bolt.

Check to see if the trolley (the part that slides back and forth on the rail and is connected to the door) is jammed against the bolt just in front of the motor unit. If so, remove the bolt and run the door until it is closed. On the side of the motor unit there is an 'up limit' control. Turn this 3 turns in the opposite direction of the arrow printed on the cover. Be sure to replace the bolt.

goto http://www.garagedooropenerguide.com/installationmanuals.html

download the pdf for the unit that is closest to what you have, go thru the diagnostics.

Hope this helps

GOTO http://www.liftmaster.com/consumerweb/service/manuals

DOWNLOAD THE MANUAL FOR YOUR UNIT.

CHECK OUT THE DIAGNOSTIC SECTION.

HOPE THIS HELPS

If you can press and hold the wall button and the door will go down, you have a photo eye issue. Check the photo eyes at the bottom of the door.