My garage door will only close to about 80%, and then reverse itself by opening up again. This has never happened before. P.S. This happened during the first major snow storm in our region.

It is not closing completely because either something is in the way of the door closing properly or the mechanism controlling the safety feature is malfunctioning.

It is an adjustment problem. Any obstruction and the door goes up again. So try adjusting again but don't leave space to invite rodents that will cause damage to car wiring. I am just going thru that.

unit is encountering too much resistance during closing cycle and reverses itself as if it is hitting something. You need to increase the closing pressure control to overpower the resistance. OR, clean and lubricate the rails to reduce friction and see what happens.

Sounds like you have an RPM sensor problem.

If your other remotes are working normally I would suspect first of all a weak battery in the keypad. Secondly the keypad could be getting weak and the closed door blocks enough of the signal to cause your problem. An open door lets the signal through. Normally during the time the keypad is flashing you can hit 'enter' again to reverse the door if it is closing or stop the door if it is opening.

Loosen the chain enough that you can remove it from the sprocket. Run the opener until the sprocket turns counterclockwise and stops. With the door in the open position replace the chain. You will probably need to adjust your open and close limits per your owners manual.

push again the button when is reversing it will stop

door will not close all the way. will go partway down then reverse itself.

There should be two small white adjustment knobs on the side of the unit that you turn with a small flathead screwdriver. These are the load / limit adjusters.

What it happening is it think there is something stuck under the door (like a car hood, etc)

These adjustments are VERY sensitive, so be patient while adjusting them.

try adjusted the sensor controls on the sode of the unit other wise replace the logic board
http://www.chamberlain-garage-door-openers.com/circuitboardcompatibilitychart.htm