You will find the smart/learn button on the rear of the motor unit near where all those white wires go. Press and immediately release it and then walk over and key in a four digit code of your choice and press enter. If everything is still working this will do it for you. Make sure the battery is good in the keypad.

If you decide it is a bad logic board and you think you might want to replace it yourself, I can tell you where NOT to buy it. I recently bought one from Ontario Supply in New York from their web site for $60. Unfortunately, it has turned out to be defective and they won't refund my purchase price even though I sent the defective unit back at my own cost. So, don't buy from them, they don't deal fairly in my opinion. I think you're best off just calling a local repair service and let them replace the board. If you replace the board yourself and it does not work, you're just going to end up calling a repair service anyway. Ontario Supply operates under the following web sites:

http://www.wholesalegaragedoorparts.com

and

http://www.liftmasterpartsonline.com/

In my opinion, you should avoid this company