How do you start the sims 2 over?

If you want to reset a neighborhood, while the Sims isn't running, you can go to the My Documents/EA Games/The Sims 2/Neighborhoods folder and delete the folder that corresponds to the 'hood you'd like to reset:

N001= Pleasantview

N001= Strangeville

N003= Veronaville

G001= Riverblossom Hills

F001= Desiderata Valley

E001= Belladonna Cove

Next, go to your Program Files/EA Games/The Sims 2/TSData/Res/UserData/Neighborhoods folder and copy the folder that you just deleted from My Documents, then paste it back into the My Documents/Ea Games/The Sims 2/Neighborhoods folder.

Another option is to delete the entire The Sims 2 folder in your My Documents/Ea Games. When you start up the game after doing this, it should take a few minutes and recreate the entire folder, thereby resetting the game to its right-out-of-the-box condition.

NOTE: All saved games will be lost unless you take proper precautions. You cannot "reset" a family, just the neighborhood. Delete folders at your own risk. The safest option is probably uninstalling and reinstalling the entire game and its expansions.