What is your base game version right now ?
Open the launcher and check the number in the lower left corner.
If you're not at 1.67, please update your game.
Manual links can be found here: http://answers.ea.com/t5/The-Sims-3/FAQ-Patch-1-67/td-p/67858/
My game is version 1.67
Try manually uninstalling Origin using this process: http://help.ea.com/en/article/manually-uninstalling-origin/ and reinstalling it again. I've had a very similar issue before (Dead Space 3 would run in the background and then *vanish* everytime I launched it), and this seemed to do the trick.
Still no luck. I did what you told, but Sims 3 wouldnt start like before.
