Back Camera isn't working

Start with the easy fixes. Have you restarted the phone? Updated software? Does your flashlight work? What about your front camera? Some history of the device may also be helpful as well before I start jumping into possible problems. But. Realistically in my experience, if the camera is just showing a black screen or crashes the app, but front facing camera seems to work, the rear camera is faulty and needs to be replaced. This is especially true if the flash is also not functioning since the enable signals for the flash travel through the camera/require a functional camera to be present.