My camera stopped focusing

SOURCE: F stop

Sounds like your camera and your lens aren't communicating. Have you tried cleaning the contacts on the camera and the lens mount?

SOURCE: Canon 40D not firing

Try doing a reset in the camera tools somewhere, this fixed a similar problem I had.

SOURCE: My Nikon D40 will not focus when I have it on automatic.

First I would try removing the lens from the camera. Then re attach it and see what happens. Next I would manually focus the lens from one extreme to the other, see if you feel any resistance or binding in the focus. If all else fails call the lens manufacturer.

SOURCE: Automatic focus not working

The D40x only autofocuses with the latest AF-S (and old professional AF-I) lenses. Most traditional (screw-type) AF lenses from 1986 through today will not autofocus on the D40x. If your lens says "AF-S," you're fine.
Most lenses sold today for the D40x are AF-S, and so is the included 18-55mm kit lens. Many non-Nikon lenses from Tamron, Tokina, Quantaray, Sigma and anyone other than Nikon still won't autofocus on the D40x. Try before you buy, but honestly, there isn't much the included 18-55mm lens won't do.
Autofocus systems are fast, but not usually instantaneous. You have to hold the shutter down halfway as you compose the first shot so the AF system can focus and lock, and then the camera fires instantaneously when you press the shutter the rest of the way. See Preventing Shutter Delay for more.

SOURCE: about 2-3 months ago my camera suddenly said lens

If it says lens error all you have to do is try pushing the lens back in. If that doesnt work, sorry! lol =(