Autofocus problems might be camera-related or user-related.
The D700 is a digital single-lens reflex, or DSLR, camera manufactured by Nikon. It is a professional-level digital camera that culls from a variety of features to produce high-quality images. Problems with the autofocus could be a number of issues related to the camera body or the lens, which might or might not need to be serviced by Nikon.
Dirt and Dust
The autofocus sensors are located underneath the mirror at the bottom of the mirror box. Frequently changing lenses and not being careful to always place the cap over the lens mount can cause dirt and dust to accumulate on the sensors. Use a blower brush to remove the dirt and dust.
Viewfinder Brackets
The brackets in the viewfinder do not necessarily align with the autofocus sensors in the camera. Switch on the autofocus and aim the camera at a sharp edge in the foreground, such as a street sign, with a distant background. If the autofocus works, the brackets are misaligned. If not, the camera might need to be serviced by Nikon.
Settings
Check to see if "Single Area AF" is activated. Turn it on and switch off all other AF settings. Sometimes multiple settings overload the camera and confuse the autofocus sensors.
Lenses
If none of the above solves or alters the problem, try the camera with a different lens. If the problem resolves with switching lenses, be sure to turn the camera off each time you switch lenses. The residual contact with the old lens can cause a failure with the new one. The lens might also not be fully compatible with the Nikon body, as is the case with some third-party lenses.
Tags: autofocus sensors, dirt dust, might need, might need serviced, need serviced, need serviced Nikon, serviced Nikon