Why won't my nikon d3000 focus on autofocus?

Its not even a year old
i've never dropped it
i'm using the lens that it came with from the box

it works fine on manual focus but when i switch to auto focus itll focus in and out but the shutter won't snap.
its not too dark because i'm always in a well lit room
i've tried cleaning the connections on the lens and body,
the lens itself is clean
the lens and body are both set on autofocus

i have no idea what's going on.
sometimes itll be fine then right in the middle of shooting itll start doing it and sometimes itll be it right from the moment i turn it on and sometimes not at all

Look in your user manual for help.

If you are still having problems, you may want to call Nikon for help 800. NIKON-UX