wildsue time to take it apart and to check the SD card reader. You will have to see if the broken card damaged any of the pins etc. If so, you will have to replace the card reader. You can use this teradown [guide|133466] to find the card reader, which is on the main board. Once there, pop the metal shield of the top and take a good look. Let us know what you find by posting some pictures of it with your Question. Definitely not an easy job, but doable.
[guide|21499]