Okay

If tapping on the unit restores function the first thing I would look for is a loose connection. BTW, Chamberlain makes most, if not all, of Craftsman openers.

The feature of having the motor unit lightbulbs come on automatically when you walk into the garage, is a feature that has only been on the market for about 5-6 years. Not all machines have this capability built into the logic board. If your machine has this capability, the only way you can turn it on or off is with a "three function wall switch" This means that in addition to a button that opens and closed the door, there are two other buttons on the same wall switch. One is marked LIGHT and the other is marked LOCK. These two buttons MUST be there in order to do this. To have your lights come on automatically when you walk into an open garage, you must START with the lights ON. If you don't want that feature and you want to turn it off, you must START with the lights OFF. To turn the feature on, turn the lights on manually with the wall switch, then press and hold the LIGHT button for about 10 seconds until the motor unit light bulbs flash. Now, if the light bulbs are on, manually turn them out and then walk out through the open door. The light bulbs should come on. To disable this feature, start with the light bulbs OFF and everything else is the same

Take off the cover and I am sure you will find the drive gear is bad. You can replace it. A new one comes with instructions.