You have accidentally deleted a photo or wiped your card.
Oh dear, how sad, never mind.
Well not all is lost, these files may be able to be recovered.
There is clever software out there that you can down load for free and this will recover your data.
If you have a full card and delete photos to make space, then fill the space with more images, then yes you would have lost your deleted images, but when you delete images it is the counter/index which is deleted, not the image so the image could be recovered.