Nikon D3100 - Help (20 characters)?

I don't usually use liveview on my camera. But how come when i don't use live view i can't change the AF-area mode?

The AF sensor is built into the prism finder. I. E. It works best when the mirror is down.

It is the same reason why your screen blacks out when you are focusing. When you are focusing in live view, the mirror goes down and the screen goes black for a moment. Once the camera is focused, the mirror goes back up and you can see everything focused again.