Make sure you put the black cup back on the end of the motor shaft and that it is pressed all the way on. Make sure the RPM sensor is plugged in. If neither of these are the issue, then you probably did not have the motor shaft pushed all the way back when you tightened the coupler after replacing the worm gear. Loosen that coupler up and from the front of the motor (opposite end in which the coupler is on) push the shaft back as far as it will go. Hold it there while you tighten the coupler back up and then try it.

Thanks, it's the black cup that I did not install is the culprit. I am just wondering what the black cup do with the motor. Anybody knows?

The black cup interrupts the infra red beam on the printed circuit that sends a pulse to the logic board. Without the pulse the logic board reverses the direction of the door when it is closing. When the door is opening it just stops where ever it is.

Thanks for the information. Have a wonderful day!!!