If you find that your gate opens perfectly fine and doesn't close, this could be why. On your main control board there is an NC light that should be on at all times (see image B below). If this light isn't on then the control board thinks there is an obstruction within the gate way area and will not allow the gate to close.
There should be a small loop wire (see image C) between COM and NC on the control board. If the loop wire is there then just tighten up both screws. However, if the loop wire is missing, just add a small piece of wire/cable between COM and NC. Once the screws are tightened up, the NC light should come on. Now activate the gate with an accessory to check that the gate will close.
