Earlier this year, the AF-S Nikkor 18-70mm f/3.5-4.5G ED that I frequently use stopped zooming. Since this is known as an excellent lens, and the zoom was the only problem, I decided to attempt to fix it. Working on lenses is usually a hassle, so I was pleasantly surprised at how easy it was to fix. It turns out that there are three screws that sometimes come loose. I just had to remove the rubber zoom ring, remove the screw under the rubber, then tighten the internal screws that is loose. The loose screw is marked by the green arrows in the picture, but for others it could be the screw marked by the red arrow, or the one on the other side of the lens.
Once I tightened the screw, I had to spend a good bit of time aligning the zoom ring and the inner ring to close the lens. Seeing someone else’s description of the proper alignment helped. I eventually realized that the lens was zoomed out a little too far to make everything align. To open the lens, you have to zoom to 70mm, but to put it back together, it is much easier if you back off of 70mm a little. Once I realized this, it lined up easily, and the lens is back to the way it should be.