Just bought a used Pentax ZX-7 and separately bought a used Pentax SMC A 35-80 f4-5.6 lens. The auto focus does not function, I have the white dot set to "A". The camera will sense when it is in focus but it will not focus automatically. Does this sound like I have a malfunctioning lens? or is something like this commonly a problem within the camera body? I have ordered a new Tamron lens but it has not arrived yet for me to test on this camera body.