40 DX - blurry pics

The lens is out of focus or the shutter speed is too slow, to determine if this is a defect or failure, mount the camera on a tripod and use the self timer or remote cable (if you have the remote cable) to take exposures while autofocusing on a neutral colored object such as a beige item,

if they're still blurry then manually focus the camera and try again.

If they are still blurry and your Nikon has a diopter focus adjuster (this is typically in the rear next to the viewfinder where you focus your eye), set the diopter to neutral and manually focus again.

If they are still blurry, remove the lens and using a cloth dampened with high percentage or denatured alcohol, clean off contact rings since this is where the lens and the camera body communicate and transfer focus data.

If they are still blurry, then use the same cleaning method for the contact ring of the camera body.

If they are still blurry use a different lens and repeat the first two steps.

If they are still blurry then you may have a smudged and dirty sensor, this is the part which actually registers the image and should be cleaned by a professional.

If you are so brave to, you can use the cameras feature to lock the mirror and expose the sensor, this is typically only done to perform a dust cleaning using light blasts of clean air and using solvents on the sensor is dangerous.

If you choose to do so anyway, use a bright flashlight and look for anything that appears to be smudging, if it isn't apparent then your camera or lenses are likely in bad need of maintenance.