My nikon d3100 won't autofocus?

I've tried so many different things and can't make it auto focus. It only focus's with the shutter half down.
will i need to reset it? If so what does this mean and how do i do it/
thanks

Added (1). No, this camera DOES autofocus by itself.google it.

Added (2). Seriously guys google it. I know people with the camera

Press the 'take photo button half down, that will autofocus normally

Well, thats how the camera works - Like all digital cameras, it doesn't autofocus by itself, you have to half-press the shutter release button…

That's normal, every single autofocus stills camera ever made works in that way. It only autofocuses continuously when recording video.

Sorry, but you are wrong. You must press the shutter release button halfway for the autofocus to engage.

Your camera does not have an internal autofocus motor and therefore only autofocus with af-S lenses, and, needs to have the button pressed halfway to engage the af motor in the lens.

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The video you provided is demonstrating the AF-F setting which will continously auto focus in VIDEO MODE ONLY. You would know this if you had bothered to read the review rhat linked to that video or read the instructions that came with your camera.