If the gate is not working, first make sure that the gate is receiving power and that all the peripheral equipment that may be connected to the gate is working. If all the equipment doesn't work, that means that the gate is probably not receiving power. Thus, make sure that the electrical mains are on and that all the wires are undamaged. Replace the damaged wires.
If the transmitter has a special light on it, make sure that it is on. If the light doesn't work, the batteries in the transmitter may be dead, so replace them. Try to open the gates by entering the access codes into any access controllers that are on the gates. Find out if all the peripheral equipment is working correctly, and replace the devices that don't work.
If it is a sliding gate, examine the path on both sides of the gate, and make sure that there isn't anything stuck under the gate on standing in its way. For a rolling gate, move something in front of the gate, and listen for a clicking sound. If a sound can be heard, the gate doesn't work because it's detecting obstacles. If there is no noise, the safety beam might be broken. Examine it thoroughly, and fix the problem if it is possible.
Most electric gate repairs have to be conducted by a professional; however, the repairs mentioned above are possible for an amateur to perform.