Bought a Sigma DG 70-300mm 1:4-5.6 autofocus for my Nikon D40. When the lens is attached the settings get locked on MF. Is there anything I need to adjust to fix this problem? Charles

Could you be a little more specific about "does not work"? Does the lens not fit? Can you not view through the lens when it's attached? Does it not autofocus? Does it not meter the exposure properly?

That would depend on what you mean by "ok." Assuming you get the lens with a Nikon mount, it will fit onto the D40 and meter properly. However, the D40 lacks an autofocus motor and thus this lens will not autofocus. You can still focus manually.

Yes, it will fit. However, lacking a focus motor, it will not autofocus on the D40.

The Nikon D40 does not have an autofocus motor, relying on the lens having one. This Sigma lens does not have such a motor, relying on the camera having one. Nikon designates lenses with an autofocus motor AF-S, Sigma calls theirs HSM.

Unfortunately, you don't. The D3000 does not have an autofocus motor; it relies on the the lens having one. This particular Sigma lens, unlike its Nikon equivalent, does not have a motor.

Nikon calls their lenses with an autofocus motor AF-S. Sigma calls theirs HSM.

You have to make sure you bought the sigma lens with a NIKON mount. Sigma makes a Sigma mount as well as a Canon mount, of course neither of those mounts will work with your camera. Also you must also make sure your lens is the Sigma 70-300 HSM (/Hyper Sonic Motor) or it will not AF on the D40. I just bought this lens from Abes of Maine and I love it on my D40.

hi ! iam too a D40 holder,u can opt for AF-s versions or HSM sigma,both of them autofocus on d40,can go for 18-200 AFs VR or if u need still longer end go for 70-300 but it is costly than the sigms 70-300APO DG HSM MACRO..,its a much better reviewed lens and dont forget the cost..anyway do some research before considering..good luck

Your 28-90 AF-D lens can't autofocus with the D40, which requires AF-S lenses with a focus motor in the lens. Sigma lenses with "HSM" (HyperSonic Motor) in the name also have the focus motor.

All Sigma:
50-500mm f/4-6.3 DG
50-150mm f/2.8 EX DC HSM
70-200mm f/2.8 DG MACRO
80-400mm f/4.5-5.6
100-300mm f/4 DG
120-300mm f/2.8 DG

Unfortunately, this lens is not supported by the D40 due to Nikon's unfortunate decision to leave out the autofocus motor from this camera.  This is why I tell folks not to waste their money on the D40 - access to the many, many, many lenses that Nikon has made over the years, many of which are available used for a substantial savings, is lost on this camera.  The only Nikon lenses that work are AF-S lenses, and some third party lenses that have their own internal motors.  I got a list of Sigma lenses that are compatible with the D40 for you:
The list of compatible Sigma lenses for the Nikon D40 as of the current date is as follows:

• 10-20mm F4-5.6 EX DC
• 12-24mm F4.5-5.6
• 17-35mm F2.8-4 DG
• 50-500mm F4-6.3 DG
• APO 50-150mm F2.8 EX DC HSM
• 70-200mm F2.8 DG MACRO
• 80-400mm F4.5-5.6
• 100-300mm F4 DG
• 120-300mm F2.8 DG
• 300-800mm F5.6 DG
• 14mm F2.8 EX
• 30mm F1.4 EX DC HSM
• 150mm F2.8 EX DG
• 180mm F3.5 EX DG
• 300mm EX DG
• 500mm EX DG
• 800mm f5.6 EX DG

from here:  http://www.imaging-resource.com/NEWS/1177682545.html
Sorry for the bad news.  The cheaper thing at this point may be to sell the D40 and get a D80.  I personally have a D70S, but that is no longer made.