I suggest that you wipe all the Sims 3 games from your computer and install everything again. It's always a good idea to do this before installing a new expansion pack or stuff pack. It's just good game maintenance.
You can find all these instructions on the
Technical Help Board. Follow the instructions step by step. You need to be sure to save a backup copy of your game files. Then uninstall all of the Sims 3 games in reverse order: HELS, WA, Base game. For good measure, do a Disk Cleanup and Defrag on your computer. Then install each of the games in the order they were released: Base, WA, HELS, Ambitions.
Also, be sure to have your product code handy for the reinstall. You won't be able to install anything without them. You can find the product codes printed on the back of the booklet that came with each DVD.
Good luck and let us know if it works!