HELP! My Sigma 24-70mm 2.8 lens' AF motor doesn't seem to work

I have a Nikon D3200 and bought a Sigma 24-70mm f/2.8 EX DG Macro Nikon Fit Lens. The manual focus seems to work fine, but Autofocus doesn't work at all--there's no sound of the motor even trying to work; it's like the button isn't sending the right signal to tell AF to work. I don't have a manual, and can't seem to find one online. How do I get my Autofocus to work?

I don't know for sure, but you might have bought the older version of Sigma. This version did NOT have a focusing motor in the lens. It was focused by the camera's focus motor. Unfortunately for you, your D3200 does not have this motor.

So you have 2 choices: sell that lens or exchange it, or, get a higher lever Nikon. The D80, 90, 300, 7000, 7100, 7200, 600, 610, 700, 800 etc have the focus motor in the camera.

Thanks! Which Sigma 24-70mm 2.8 should I get that will work? How do I know of it's the newer model? Is there a specific model number I should be looking for?

The Sigma lenses that have a focusing motor have the HSM marking on them. You can google Sigma lenses with focusing motor to find out more about different models who have it.