Hello Sharon15,
If those images have been edited in any way on the computer, the camera will no longer be able to display them. Accessing them using a card reader on the computer could cause this as well. I would suggest trying a different card in the camera or formatting the card that you have to test it further. When the card is formatted, all images and data on the card will be erased. Even protected images will be erased, so make sure there is nothing you need to keep. If necessary, transfer the images and data to a computer, etc., before formatting the card.
