Re: where do i find the serial code from a steam download

@JuliaMarasha  Are you going to play through Steam or Origin?  If Steam, I'd be interested to know whether you can download any items from the Sims 3 Store.  Now that your Origin account owns the game, you have access to the Store: just sign in with the same email and password you use for Origin.

Even if you don't want to buy any store content, you could try installing Riverview, which is free:

https://store.thesims3.com/riverview.html?categoryId=12642

But it's encrypted, like all other store content, which is why I'm curious whether it would work on your setup.

I had the same problem as you, but as soon as I bought DLC for the sims 3 on Steam, I got the CD keys option.. I only got them for the DLC but when I used them, somehow it automatically installed the base game as well.. Really weird...

So after reading what you said I tried again to enter all my dlc keys in without caps lock (I read that caps can mess it up) and weirdly enough they all worked this time. Although I was having the same issue as everyone else by getting the “null” message before, it worked perfectly fine this time. Though the sims 3 base game isn’t there and the CD key indeed does not show up on steam keys. I just don’t understand why only the base game key isn’t there? I even tried to regedit to find the keys but alas all my base game says is %CDKEY%, whatever that means 

@BellowYellow  The base game key doesn't show up because people were abusing EA Play in Steam to acquire keys to older games, so Steam pulled the keys for affected games rather than coming up with a more nuanced approach.  You can try contacting Steam support to request your base game key, although I'm not sure whether you'll get any help.

Someone else posted that this helped them:

https://answers.ea.com/t5/Technical-Issues-PC/Sims-3-pets-i-can-t-find-my-registration-code-in-steam/m-p/10242755#M245751

Did you look at that specific entry?  There are two entries for the Sims 3 base game in the registry.

That’s actually good to know. I assumed something like that was going on. Just sad it had to be that way. Fortunately though I think I figured it out. As long as you can at least put in one DLC key into your sims 3 account game register it should register the original sims 3 base game in your origins games along with the DLC’s . So if you have the origin app on your computer you can go ahead and start installing the base game + the DLC’s onto your computer through there. So you don’t even need to register the base game onto the sims 3 site as long as you have any DLC. For anyone out there struggling with this issue (since I found no other platforms helping with it) I’d recommend to put in any DLC key into thesims3.com. Don’t worry about not having a base game key if the DLC keys work for you. After that just go to your origins app and the sims 3 base game plus all your DLC’s should be there to install. So for anyone unwilling or unable to contact EA support id recommend trying this first. Hopefully you get to play some sims 3 soon!

ps. If you’re putting the key into the site in all caps and it’s not working, I’d reccomend to try putting it in in lower case with no caps lock. It worked for me