Failure to activate the AF is likely to mean that a trip to the service centre is unavoidable, but it still may be worth a quick check of the basics. Some lenses will have a switch for AF or MF and the camera also needs to be set to one of the AF modes, rather than to manual focus. If your camera has an ‘AF-ON’ button on the rear, top or right side of the camera, it is worth checking to see if this activates the AF instead. If it does, the issue may be solely with the shutter-release button, rather than a more major AF problem. Better still, it may be that you have unwittingly selected a custom setting that has activated this button for AF, rather than your shutter release. If you don’t know where to find this option, a quick reset of your settings should rectify it.