It happened to me because I used it in the swimming pool (underwater....) and next week started to frozen and finally didnt respond.
I put it in a dehumidifier (it can be a single sealed box with a dehumidifying tablet that you can buy for ~€2/$2) and leave it for at least 48 hours, and now It works again
(the first few minutes it may be a little slow, but then it will be fine, like the first day).
Do not do as other people say of using a hair dryer, it can even be dangerous (the back is made of aluminum, so it can hurt your hand when it is hot, like it happened to me :-( )
Good luck!