Focus problem: Sigma 120-300mm f2.8 APO EX DG OS HSM for Canon with 550D camera

[buckenmeyer]

Hi,

I bought a Sigma 120-300mm f2.8 lens (for Canon) for my canon 550D. The lens doesn't focus at all.

If I put on automatic the camera makes noises like its trying to focus and after a while it takes the picture all blurry.

If I put it on manual focus and manually turn the focus ring it does nothing, looks the same through the camera, I can turn it and turn.

Is their a compatibility problem? Is it broke? A setting I need to change on the camera?

Yes I'm a newbie. The lens is for taking sports pictures.