Re: Transferring my Sims 3 data(specifically expansions) to a new computer

@NiceGirl2004  You can't directly transfer the installed files from your old computer to your new one; appliations won't work that way.  Just to be sure, have you tried to download your packs?  Open your Origin library, click on the Sims 3 icon, select More > Expansion Packs (or Stuff Packs), scroll through the list, and see whether you have an orange Download button.  If you do, the packs are on your account, and all you need to do is download them manually.

If the packs say Buy Now, did you ever specifically register your discs in your Origin account?  If not, or if you're not sure, you can try registering them now.  Even if you've lost the product keys, you can probably still find them on your old computer.

https://sims3.crinrict.com/en/2013/09/how-to-find-your-serial-number.html

Otherwise, maybe you can try installing your packs via disc again.  Origin is supposed to be able to manage a mix of disc and digital installs, although it doesn't always work.  (If your base game disc was manufactured before September 2012, you can even install without Origin's involvement.  Let me know if you want instructions.)  External disc drives are cheap these days, and if you don't want to buy one right away, maybe you can borrow one from a friend to see whether the game works.