Nikon d40 am having a plobrem with the auto focus and the camera won't take pictures whe on auto settings. if you focus manually and the subject is clear , the camera will operate, but will not operate when the subject is out of focus.

The letters you're referencing is the M/A (manual / auto) focus switch. The lens has this switch and operates in Auto Focus mode when set to "A" and manual focus mode when set to "M".

You have to manually focus on the subject when in letter "M". If you do not, the result will be out of focus. From your description, it sounds like the camera / lens combination is attempting to focus and operate the shutter in auto, and focusing in manual; but due to some type of damage resulting from possible mishandling, exposure to dust, dirt or even moisture is interfering with the successful completion of the process.

You could isolate the problem to determine if the cause is in the lens or camera by simply attaching the lens to another compatible Nikon camera or placing a different auto-focus lens on your D40. The problem will either stay with your D40 or follow the lens when attached to a different camera. It is also *possible* that due to numerous attempts of auto-focusing with your D40 & lens combination, that both the lens *and* the camera have been damaged. If the problem is severe enough, the problem in the failed device could cause failure in the otherwise normally working device, too.

You might be best served by contacting Nikon Service & Support below:

http://www.nikonusa.com/Service-And-Support/Service-And-Repair.page

You also said you lost your manual. You can download the manual for the D40 directly from Nikon in your choice of English, French or Spanish from the link below:

http://support.nikontech.com/app/answers/detail/a_id/14157/session/L3NpZC9YRTgxQVpKag%3D%3D/kw/D40%20manual/p/19%2C334/c/187/r_id/116678/sno/0

Good luck!

Are you in auto mode? If it is manual then it is possible that the settings are not correct for the light. You can look at the meter to see what the camera thinks about the exposure.

It sounds as if your subject is too dark. Does this happen when the area is brightly lit? Does the flash fire?

What lens are you using with the D40? Is it an AF-S lens? And is the Mirror Lockup on? Chech the Custom Settings menu. If mirror lockup is on, turn it off.

It's a report saying that the camera is busy doing something. It can hapen when you have taken a photo and the camera is busy processing but I find it happens when in auto focus and the camera is having dificulty due to distance from subject or light. Try switching to manual focus, moving further away from the subject or casting more light on the subject.

Try Blow cleaning the Memory card slot ... sometimes dust does that

I assume the lens had the impact. The 18-55 lens has the built-in motors for auto-focus.
Try switching to manual focus (on the lens). If this works, the lens may not auto-focus anymore.
Try it and let me know.
cheers,

Camera wont let you take a picture until focus is locked, why are you using M (manual focus) if you expect autofocus to do it for you? In M mode it is up to you to focus correctly or camera will not take the picture.

When the camera is in auto focus mode, it will not take the picture until it locks onto a subject. If there is not enough light, the camera will "hunt" for something to focus on. Since it can't define any edges, it won't allow the shutter to release.

The D40 base model does NOT have a powered focus lever for autofocus, so if the autofocus is not working, suspect the lens.

Same here :( cant got working

Chances are good that it's not your camera, but your lens. In a darker atmosphere, you need a fast lens, meaning you need a lens that has a wide aperture (1.4 to 2.8) I'm guessing you're using a lens thats' 3.5 or larger. (Yes, the larger apertures have the smaller numbers)

If your camera was spending all it's time moving in and out trying to focus, it's probably because there was not enough light for the camera to distinguish a focal point. Same thing happens when you shoot a solid blue sky. No focal point.

Help me understand by telling me what lens you're using and what settings you were using on the camera.