Thank you both for replying. Sadly, neither of your suggestions have worked. I have searched for another TS3 folder by simply typing in the name, but the one in my Documents is the only one I can find.
I'm not sure if the package files work, but I know for sure that the sims3packs still don't show up in game. I have checked my Downloads folder in my TS3 folder, and the content seems to be right, although I'm not sure about that. There are 3 files in there: nav.bin, wl.bin and FSIViewCountTracking. Are those supposed to be in there?
The next step will be a complete re-install, I'll probably do that next weekend. I hope that'll fix the problems.
Thank you for helping me, and if you have any other suggestions, I'll be happy to hear them. :)