Either some crud had become wedged into the button crevices, or was hit with such a shock that the underlying circuit board has become damaged/crushed. If, after taking a good look at the button periphery, you don't see any crud worth scraping out, I would say it's a goner and will have to be trashed. Repairing it would most likely be futile unless you are or know someone who's adept at surface mount rework. Sorry. ☹️
