Hi I bought a second hand SIMS 3 pc game from a pawn shop.

Which edition is it ? Hee's an overview of the existing ones: http://sims3.crinrict.com/en/2014/02/sims-3-base-game-versions.html ?

If you have the old one, you can just install the game without registering and play that way.

If it's the newer one, take it back to the shop and get your money back.

@Jeanne_dub You can not un register a sims game code as once the code is accepted that code is locked to an Origin account. If you get the pre 2012 version of sims 3 you may be able to use the old code on thesims3.com but you probably won't be able to use the store or add any packs. Origin is like Valve's Steam. Many (I think most if not all) used game stores have stopped taking in games like the sims and otheer games that need to be registered. I feel you may see more services that will make you play to play (monthly charge) so buying used games may disappear all together.