I bought a used Nikon D610, it was working fine and then suddenly  one day the autofocus stopped working, the camera focus switch is on auto and the lens is also on auto option, and the focus is assigned to half shutter press, but still the camera is not focusing, and it seems like the camera is not even trying to focus, the focus indicator just stays red when i press the shutter button half way. and the control panel does not even show the af mode and i cant even change the af modes.