WHAT IS WRONG WHEN CAMERA IS DEAD? THE BATTERIES

Possible solutions are:
card or battery door tabs for cut out switches are broken or the micro switches are damaged.
Blown fuses on the board. There are several fuses on the main board and power board and to determine which one has blown you can connect an ac adapter to see if your camera will power up via mains. If it does then the fuse for the battery has blown. If neither will power up your camera then the main board fuse will have blown. To check the fuses you will need a service manual, not an owners manual, for the locations and correct types of fuses.