Check the easy things first
Replace the remote battery and try again. Stand close to the gate and press the button. If one remote works and another does not, the problem is the remote and not the gate.
Look at the gate side
See whether the controller shows power. A tripped switch or a loose antenna can shorten range. Metal objects or new equipment nearby can also reduce range.
When to call
If no remote works, the gate moves oddly, or you hear a motor humming without movement, stop and ask a technician. Do not open the control box or bypass safety devices yourself.