LiftMaster garage door opener won't open. When push button (from either remote or "door-bell" style button on wall), unit makes a slight humming sound for a couple of seconds, then nothing...?

Is the door stuck in the open position?

You don't unlock anything to program the opener for the remotes. If everything is working you do this:

Press and hold the button down on the remote while you press and immediately release the smart/learn button. Do this for each remote.

If when closing the door it reverses to the open position and the main light flashes 10 times it is a door sensor problem. Make sure the small light on each sensor is on and not flickering ever so slightly. (check closely) Tweak them a little even though they may seem to be okay. Check for 5vdc between terminals 2 and 3 on the rear of the motor unit. If there is no voltage or if it is greater than 6vdc the logic board is bad.

Make sure the trolley is not jammed against the bolt just in front of the motor unit.

If the main light flashes 10 times when you try to close the door it is a sensor problem. Make sure they are not flickering ever so slightly and that they are not loose on their brackets. Tweak them a little bit.

I think the trolley has jammed against the bolt just in front of the motor unit. Remove the bolt and then run the door until it is closed. With the door closed locate the 'up limit' control on the side of the motor unit. Turn this 2 turns in the opposite direction of the arrow printed on the cover. Replace the bolt.

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

DOWNLOAD THE MANUAL FOR YOUR UNIT.

CHECK OUT THE DIAGNOSTIC SECTION.

HOPE THIS HELPS

The unit is in the lock mode, push and hold the lock button in for about two seconds and the green LED should stop flashing. Your remotes should work.

Does your wall switch have a lock feature? By pressing the lock button, the remote control is disabled. A flashing light indicates this feature has been activated.

To deactivate, press and hold the lock button for 2 seconds. The flashing should stop and your remote should work again.

Have you tried to reprogram the chanel again?
Changed the battery?