I was taking pictures last night, everything was OK until I switched to my Nikon DX AF-S 55-200 1:4-5.6G ED lens. I found that the autofocus will not work. I took it off, put it back on and tried it on my neice's camera (D40) and it will not work on her camera either. I'm a bit of a beginner so I don't think I have settings wrong. Especially since my 18-55mm lens works fine. I haven't dropped the lens or anything. Any ideas on what the problem might be?