Are you saying that it doesn't rotate, or doesn't "click into place"?
Originally Posted by Wujaszek
If you look inside the back of the camera, on the right side of the lens barrel, at about the 3:00 o'clock position, you'll see a little catch. As you rotate the lens, a tiny hook inside the camera body should engage the catch on the lens. The hook is hard to see, it's behind a part of the interior; but if you push the lens release button continuously, you should be able to see it moving. If the lens does not turn far enough to engage the little hook, it will not lock into place, and your shutter will not fire. Another little bar on the 9:00 o'clock side of the lens prevents you from closing the lens unless the shutter is cocked.
Hope this helps.