Q: My iPhone 5 Camera Has Stopped Working?

My iPhone's rear camera has suddenly stopped working. When I go onto the camera application, I can see myself in the front view camera. However, when I click the icon to switch to my rear facing camera, the picture freezes and a caution mark appears in the top left corner. When I clicked this, it says that my iPhone needs to cool down before I can use the flash. But my flash is never on? And my iPhone isn't remotely warm.

I tried leaving it for a while and I also tried turning my phone off and then turning it back on again. The last thing I tried was a hard reset by pressing and holding the home and the power buttons. Nothing seems to have fixed the problem. Can anybody help?