I can't get the camera on my iphone 5 to come on

I have a iphone 5 and the past week my camera shows a black screen or a closed lens. I have got the new update, restarted my phone, forced closed the camera app and nothing will work! My front camera does work but does anyone know how to get my back camera to work?

Just update it

Hold the top sleep/wake button and the home button at the same time until your phone powers off and then shows the Apple logo (aka soft reset).

Your first mistake was buying an iPhone in the first place

It is a known issue try these:
http://appletoolbox.com/2011/11/ipod-iphone-camera-shutter-will-not-open-how-to-fix/