sims 3 base game wont install

@katsimming  Lovely.  But yes, this is to be expected with a new code.  The registry entry for the base game has the old code in it, and the mismatch causes the error.

The solution is to uninstall the game, clean your computer's registry either manually or with a tool like Piriform's CCleaner (the free version works fine), and reinstall from Origin.

I uninstalled the game, cleaned the registry and reinstalled the game but I get the same error message when I go to launch the game. Is their any other way to fix this? 

@katsimming  The most common cause of that error is leftover registry keys, either from a mismatched base game or from packs you no longer have installed.  If you want, you can look for entries manually, although this guide is a bit out of date:

https://help.ea.com/en-us/help/the-sims/the-sims-3/manually-uninstalling-the-sims-3/

If you don't find anything, try running Origin and TS3.exe as an admin: right-click on each one and select "Run as administrator."  (You can find TS3.exe in the game's program files, which by default are installed to Program files (x86)\Origin Games\The Sims 3\Game\Bin.  You can also try running Sims3Launcher.exe as an admin.)

If that doesn't help either, try doing a clean uninstall of Origin using Revo (the free version).  First, clear Origin's cache:

https://help.ea.com/en-us/help/faq/clear-cache-to-fix-problems-with-your-games/

Then use Revo Uninstaller (the free version is fine, either regular or portable) to remove all traces of Origin, except for the Origin Games folder.  Here's how:

• Quit Origin, then right-click on the Task Bar and open the Task Manager.  Scroll through looking for Origin entries.  If you find any, click on them and End Task.
• Download Revo Uninstaller from here (again, the free versions are fine).
• Install Revo, open it, and uninstall Origin.  When it's finished, Revo will ask you which cleaning method you want to use.  Select "Moderate" and then Browse.
• If Revo finds any remaining registry entries, select all, delete, and click Next.
• Revo will display "Remaining Data and Folders.  Select all of them except for the "Origin Games" folder.  (This is where TS3 and other Origin games are located.)  Delete the rest.
• Restart your computer.

Next, download and install Origin—the regular version, not the beta.  Here's the direct download link:

http://download.dm.origin.com/origin/live/OriginSetup.exe

Be sure to run the installer as an admin as well.

I followed everything you told me to do but I’m still getting the same error message. Is it possible I did something wrong or is there anything else I can do?

I reset my computer which probably wasn’t the best idea but I couldn’t find all the files to delete no matter what I did. Resetting it worked tho and I didn’t have anything important on there anyway.

Thank you for all your help. So glad to finally have my game running again!

@katsimming  It's unfortunate that it took a total reset, but yeah, there was definitely something lurking in there, even if the cleaner apps couldn't find it.  (Who knows, maybe it wasn't even in the registry.)  I'm glad your game is working now.

And I'm even more sorry that it took so much effort to get a game back that you should have had all along.  Hopefully this problem overall gets sorted out soon, because it shouldn't be happening in the first place.