Sims 3 store content dissapears

claradensmukke  Once the content has disappeared, trying to reinstall it won't help, or will only help temporarily.  Since you've already tried that, you'll need to reinstall everything into a clean user folder, a few items at a time, then transfer over your saves and other content.  More detailed instructions are here:

[Read First] Sims 3 Store guide | EA Forums - 11157679

I would strongly recommend keeping an extra copy of the Sims 3 folder with the Store content installed, as this may happen again, and it's a lot easier to restore your spare copy rather than reinstalling everything each time this happens.  But if and when this does happen again, before doing anything else, try deleting the SigsCache folder, which helps some of the time.