The D40 body can only autofocus if the lens is equipped with it's own in-built autofocus motor. If you have an AF lens which relies on the camera body having the AF drive motor then you have to use MF only. To cut cost and weight, the D40 relies on using lenses with their own AF motors.
Quantaray is a Ritz badge-engineered product, usually based on a Sigma/Tamron design but not always identical to those brands internally. As Ritz don't have a UK/European presence they're unfamiliar to me, but if it's the same as the one shown on
this website, then it definitely lacks a drive motor, the second photo down when enlarged clearly shows the mechanically operated AF coupling at the six o'clock position. Again, to cut cost, the lens shown does not have a built in AF drive motor.
If so, your only fix is to either upgrade your body or lens to versions which aren't cut price models, or to simply focus the good old fashioned way, knowing that what you've focused on is what you want and not what the camera thinks you want... ;-)
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