Most guides here on ModTheSims Wiki advise you to make a backup of your user files by renaming a preexisting My Documents\Electronic Arts\The Sims 3 to The Sims 3 Backup. Instead you will unfortunately have to redownload your sims3packs and install via the launcher.
If you do not have a backup of your user files (the ones located in My Documents\Electronic Arts\The Sims 3) then you cannot recover sims3packs using this method. While this process is fairly painless, it is written assuming you made a backup of your user files somewhere. This is useful for when you want to put CC back into you game after doing a game reinstall because you do not have to redownload all your sims3packs and install them with the Launcher.
You can recover sims3packs that you have installed very easily.
