Iphone 5 screen camera not working?

Whenever I go on my iphone5 camera the 'vault' type screen takes forever to load and when it finally opens there's just a black screen. I can't take any photos or swap it to the front or back camera. I've only had this phone for one week and the camera was working perfectly fine before and I haven't dropped it or anything. I've restarted the phone so many times but the problem is still there.
When I go on CamWow (a cam app) the front camera works fine and takes photos but if I try swapping it to the back cam it just freezes.

It seems there must be some problem with the camera. Try updating the firmware, if that doesnot help, rush to the Apple store and explain the complete process and make sure you show them atleast three other problems, you will get an exchange! Lolzz… USe the trick to get a new phone!