Sigma 28mm 1.8 AF-D on Nikon D3100?

When I attach the lens the camera won't Respond.

What is wrong?

Added (1). By not responding, I mean the camera won't turn on.

Added (2). When lens is on camera, it goes dark, but as soon as I remove the lens everything is back to normal.

In the fine print, Sigma says this, "Nikon Mount: NO built in motor lens: NOT compatible with D40, D40x, D60, D3000, D5000". This includes the D3100 and D5100 as well.

Did you do the research to see which of the Sigma lenses have a ultra fast auto-focus motor in them?

Return the lens and get one that has the HSM designation.

Here is the chart. Look for lenses with the Nikon mount "N" and that are "HSM"

Without the lens, does the camera go on? Try cleaning the contact points at both mount ends and try again. If you can get another Nikon dSLR to try it on, then maybe you can isolate the problem to the lens, not the cameras. You may need to call the store or seller.