When you can’t use the button on the wall to open your garage door, you should start by checking the power. Make sure you haven’t tripped a breaker. If you have power to the house, then there is likely something wrong with the button itself.
Make sure the the wire is not lose. You may need to tighten the screws on the terminals or push the connectors back in. If you tighten everything and it still doesn’t work, then you may have a bad wire or button itself. Start by replacing the wire to see if that changes things. If all else fails, replace the button with a new one.