@Nathiel13 I understand; this game has made most of us curse out our computer screens sooner or later.
For store content, there are a couple of obvious possibilties. One is that the file called ccmerged.package inside DCBackup has been corrupted; this file is necessary to make premium content work. But if some of your non-premium store items are also missing, the problem is probably not ccmerged. More likely would be that one of the .ebc bundles in DCCache is corrupted, and the launcher isn't reading that bundle or any of the files numbered higher than it. You can use a version of Method by Mell, described on this page (scroll down), to test the bundles one at a time:
https://sims3.crinrict.com/en/2011/01/tutorial-how-to-get-rid-of-unwanted-custom-content.html
If all of your store content is missing, try installing one file into a new game folder and see whether it works. Also, have you recently added another Sims 3 base game code to your account? Do you or did you have Origin Access at some point? Store content can "go missing" when it's attached to a code or account that's different from the one opening the launcher.
By the way, most of the troubleshooting steps here don't involve reinstalling the whole game, nor would that be necessary unless there's a mismatch between your base game code and the one tied to your store account. Usually, working with a clean Sims 3 game folder is enough.
