Nikon D3100 lens no longer Auto-Focus'?

I got my camera in October 2011, i haven't used it since December as i had my charger stolen. I finally got a new charger and now my lens (the one i got with it) doesn't auto focus, i have to do it manually. I have reset all settings my camera and it hasn't changed anything. It hasn't been dropped or mishandled so i don't know of any reason it should be broken?

Check the A/M-A switch on the side of the lens.