So I just bought Skyrim, when it asked for my product activation key, I put it in and it says it's already been used. I've checked through plenty of times and it's all correct. It isn't second-hand, it was in factory wrapping. What should I do?

Either contact Beth support directly (http://support.gamesas.com/form.php?l=en) or you need to bring it up with your retailer. Those are really your only options.

http://www.zenimax.com/contact.php.