and finally one more post (this way i should be a member again soonish, hope no one is bored of my broken game):
i think i solved the problem. I had forgotten that I had made a different type of backup a week ago. meaning that I had backed up my The Sims 3 folder on my computer rather than just some differently named game files in-game. I deleted my bugged Sims 3 folder and put my backup back in and it seems to have worked!
So the lesson is: in-game backups are only good if you want to cheat. Like if you made a big mistake / wrong decision in game and you already saved your file then you have a safe point to go back to. But those old safe files are no good if your game gets corrupted because there is a chance they will all get corrupted (at least all the ones that are connected to your current world). I still cannot believe that my empty world file got corrupted too! I mean, I had not even played in that world, Adam and eve had not moved in yet. So strange. While on the other hand there were old games in that folder that I had played before this challenge and they were all fine. From now on I will make backups of my Sims 3 folder regularly. Close call this time. phew