Nikon d3000 will focus in and out but won't snap picture?

It happens randomly.sometimes itll work just fine and others it will focus in and then out and not take the picture.ill switch to manual focus and itll be fine but i don't want to manual focus all the time. I take off the lens and wipe off the connecting parts and it doesn't do anything. Its very new, and i don't use it much.i've never dropped it. I have no idea what it can be.switching settings doesn't hep either.

The symptom you are describing is known as "focus hunting".It happens when there's either not enough light to find focus, or there's no texture or contrast where the focus points are located. When focusing, center the focus point you are using over an edge, or a high contrast area, half press the shutter, recompose your frame while holding the shutter halfway down, then fully depress the shutter.