Why will my camera not let me take a picture sometimes nikon d3100?

I have a nikon d3100, and i use it on auto. Sometimes i press the button and it doesn't want to take a picture. It focuses and the i can hear the lense focus but it just won't take… Its awkwood when there's some 1 waiting and it will not work.

Is it when the light is low? The camera may not lock on the focus and be going back and forth between to areas that are close. Try locking the focus on the subject's eyes and recomposing the shot.

Then maybe you should take the time to learn how to use your camera on manual and stop letting it tell you what to do.