Maybe the battery is dead.

Motor units have batteries?

Sorry I probably did not explain correctly. I don't think the Motor unit has batteries in it (if I'm wrong, please let me know). So the battery in the remote control IS new. When I pressed the "learn" button, the red light just don't blink as it should (to wait for the user to press the button on the remote to "pair"). Any idea what might have caused the "learn" button to NOT blink? Thanks!

Try "erasing" it by holding it for 10 seconds, and make sure your safety eyes are not blocked. Then make sure you follow the protocol per the steps for reprogramming. I do these quite often, and IIRC some have not lit and given frustration. After some retrying they have always worked - the button is directly on the board and is seldom used - so if it didn't work there probably would be a much larger problem with the motor electronics.

@3onthetree: "Motor units have batteries?"

Uh, no. I thought the button was on the remote.