I will give you the steps that you can isolate whether memory card or the reader has malfunction. check the memory card with external card reader by connecting to computer if card really bad it will alert either error or unformatted (make sure write protection of the card is off if exist). When you format in computer successfully it can work in camera too. If issue persist in camera side you can try another card and next step will be hardware repair of camera reader. hope it will help.
Good Luck