As the little red light doesn't shine when pressing the button the contacts on the switch in the fob is probably dirty or there might be a dry joint on one of the connections somewhere board.
Take it a part and take some good photos both sides on the board, there might be something obvious or if you're good with delicate work take the metal casing of the switch that's on the board off and clean the contacts.
Take it a part and take some good photos both sides on the board, there might be something obvious or if you're good with delicate work take the metal casing of the switch that's on the board off and clean the contacts.