@twinkleberrypie How did you buy your game? These days, packs purchased through Origin don't come with serial codes of their own; Origin itself handles the authentication (at least in Windows). So if you're planning to reinstall through Origin, you won't need any codes—just sign in, download the base game from your Library, and then click More > Expansion (or Stuff) Packs to get a list of your owned content.
The only problem is if you're looking to install into mac OS, in which case you'd need to contact EA and ask for codes.
https://help.ea.com/en/contact-us/
P.S. There are still a few of us here, even if this particular thread has been dormant for several years. If you have other questions, there's a thread specifically for new members who can't start their own discussions yet:
https://forums.thesims.com/en_US/discussion/893122/thread-for-new-members-to-post-their-sims-3-game-issues#latest
