How do I register my game?

Hi everyone!

Does sims 3 and all EP's work on Windows 8? I got the Sims 3, Sims 3 Master Suite Stuff and Sims 3 Pets for Christmas and I registered them onto my Sims 3 account on sims3.com. I used the product code/serial number to register them before I even installed them on my laptop. But now when I try to install it to Origin, I put my code in and it pops up with 'This code has already been used'  (its along those lines) and I've tried EVERYTHING possible to get it to work. I've tried to do it from the Origin website and it just comes up with the same thing.

Have I done something wrong? I'm so confused.