Instead of uninstalling/reinstalling your game you can go to Documents/Electronic Arts and drag and drop the entire Sims 3 folder onto your desktop. If you still have your packages folder in the old location (program files), drag and drop that onto your desktop too. After doing this run your game and it will be forced to recreate the entire Sims 3 folder and you will have a new clean game as if you had just installed it and never played it yet. This is much easier than the uninstall/reinstall process. If you wish you can return the packages folder if you know all the items are safe or you can pick and choose which ones you wish to return. By having your old Sims 3 folder still on your desktop you still have all your downloads stored in that folder that you can still put back into your game if you wish.
Personally I have an external hard drive that I put the Sims 3 folder onto instead of my desktop.
This can also be a good method of backing up your game, copy the Sims 3 folder and paste it onto an external hard drive. If the game suffers huge problems you can replace the Sims 3 folder on your computer with the backup one on the external hard drive.
