Memory card problem

okay so i took out myy memory card on my dxg 305v camera and then i tried to insert it back in but it only lets me take like 20 pictures and saves it to the camera not the memory card then when i go to upload it it reads the memory card and the camera how do i get pictures to save to the memory card again? I dont have the directions because it was given to me by a friend. ): please help?