I've had my Nikon D5000 for about two years now. It has never failed me! I have only two lenses, the standard 18-55mm lens and a 70-300mm lens I received about two years ago. I've never had a problem with these lenses until recently. I was on holiday in Prague and I had only brought my 18-55 with me. Because of the heat (40 degrees or so) my camera kept saying "lens not attached" but soon began functioning once it had cooled off. Now that I am back home, trying to use my 70-300 is a pain. It keeps saying "Lens not attached" no matter what I do, I've cleaned the connectors and rotated the lens around but nothing works and it's upsetting!! Any ideas??