My Nikon D5500 will no longer autofocus. It is a brand new camera with hardly any use. My neighbor, who has vast experience in photography, attached the macro lens, took a few shots, and then it stopped autofocusing. What happened?
With most Nikon cameras and AF lenses with focus motors in the lens, there are switches on both the lens and the camera that must be turned on for AF to be enabled. If there's not a physical switch on the camera (usually in the area near the lens release button that must be pressed to remove the lens), then it is probably buried somewhere in the menu.
If you've checked and AF is enable by both the camera and the lens, then either the camera or the lens is not functioning properly. Ascertaining which is as easy as trying another AF lens on your camera and/or trying your AF lens on another compatible Nikon camera.
Try pressing the AE-L button on the camera (it is located around where your right thumb rests). If the camera focuses, this means that your neighbour probably assigned that button to act as AF-ON and forgot to tell you. This is useful in certain situations when you want to decouple the focus from the shutter button and in this case, pressing the shutter button halfway will only lock exposure (depending on your settings).