AF 20mm f:2.8 D don't autofocus accurately. It focuses always behind the focus point.

Use autofocus if you have a AF lens on it.

Usually you get a kit 18-55 AF lens that has a A/M switch on the side. The switch should be facing the A side so it's set on autofocus. Then you have 9 points on your viewfinder, those are the autofocus points. It should usually be set to center, because you usually want the object in center of your photo to not be blurry.
Remember to press the shutter button halfway and give some time for the autofocus to focus. Then you can press it all the way, you should have your photos nice and clear.

If you happen to have a manual focus lens, you should be watching through the viewfinder and turning the focus ring on the lens and determine if your object is in focus. It's hard at night, but get some practice at home when you have some more light so you get more familiar with the focus.

The D90 has three different autofocus modes. In the AF-S mode it will not shoot until it has focused. In the AF-C mode it will shoot when you press the shutter release button even if has not focused. In the AF-A mode the camera switches between the AF-S and AF-C modes so either can apply.Also, bear in mind that the camera doesn't really know what you're taking a picture of. It may focus on something other than your subject. If you're in the single-area AF mode then you control which of the eleven focus points the camera uses. In any of the dynamic-area AF modes the camera decides.For full details on how the various modes work, please consult your manual. You might also check out the Nikon D90 video tutorial.

The D5000 does not have a focus motor in the body, relying on the lens to have one. The old 70-300mm G lens does not have a focus motor, relying on the camera to have one. Thus, this combination will not autofocus.
The newer 70-300mm AF-S G lens, as well as the even newer 70-300mm VR AF-S lens, do have the autofocus motor and thus will autofocus on the D5000.

Hi, It wouldn't autofocus on the D5000 as the body doesn't have an auto focus motor in the body and since that lens is AF, not AF-S, it won't autofocus. It should autofocus on the D7000 though, how far away are you from the object you're trying to photograph?

The lock that's around the 4-way button that moves the AF point will stop it from moving. The AF switch (says C,S,M) on the body below the lens release button gets knocked to manual and turns off the AF

The d60 needs Auto focus lenses(Ones with motors inside the lense) it doesn`t autofocus on other lenses. this was done to reduce the price of the camera body

Hope this helps

what i do is usually put it onto manual focus then back to auto focus, what it may be is that you are using the wrong lens for your subject :/

Sounds like you need to get your camera fixed by Nikon.

However, you say the auto focus stopped working, you didn't switch to a lens that uses a mechanical focus linkage do you? The D40 only supports lenses with AF-S or AF-I type autofocus drives. AF-D and AF-G types without AF-S or AF-I don't autofocus.

Also, check that the A/M switch on the lens is in the correct position.

Manual focusing is quite difficult to do accurately with an AF camera. The screen inside the camera is not optimized for this. If you are sure you are focusing accurately but the pictures you take are still out of focus, the mirror may need adjusting. I can provide further info on this if you require, but if you're within warranty, i'd recommend that route first.

I had this problem awhile ago - you must have accidently adjusted the focal area - it is sooooo easy to do without realising it. Here is what I was told:
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Most likely, you have changed the AF point, which only takes effect in the creative modes (Manual, Av, Tv, P, etc)

There should be a button on your camera that has a grid like pattern above it, like
-
- - - - -
-

or so. press that, look through the viewfinder, and move the shutter or rear wheel, you should see the different AF points like up in red, and as you turn different ones will light up, and eventually all of them. also, you can look on the screen on top (or back, if its a rebel) and it will show you which ones are selected while in that mode, instead of looking through the viewfinder.