CryBabyMel22 The InstalledWorlds folder only holds data for the worlds you've installed through the launcher, so Store or custom worlds. The data for Sunset Valley and any world that comes with an expansion is within the game's program files.
The first post of this thread covers the causes of the "serious error" message, and OneDrive is the problem most of the time. But it sounds like it's possible that some of your expansions aren't loading either. So please open the launcher's Expansions & Stuff Packs tab and uncheck and re-check all the boxes. If some packs are missing, let me know which ones.
Please try the suggestions in the first post until a new save loads, check it to make sure all your DLC is loaded, and then you can go back and try to load your previous save.
Flora-Rienhold This is a system issue, not a Sims 3 issue, so there's nothing for EA to fix. Did you try playing in a new, local, admin Windows account? If not, please do so now. Even if you don't want this to be your permanent workaround, it's important as a test.
