Hi, A few days ago, I turned on my camera and it wouldn't focus-- neither Auto or Manual. I took it off, put it back on, and it worked again. This evening, I turned the camera on, and it did it again. Except this time taking it off and putting it back on does nothing. Neither auto nor manual. My 20mm lens works fine, so I'm pretty sure it is the lens and not the body. What do I do?