If your Sims 3 saved file didn't load at startup, you can recover it easily. Start by exiting The Sims 3 game. Go to C:\Users\Rit\Documents\Electronic Arts\The Sims 3\Saves in Vista or C:\Documents and Settings\username\My Documents\Electronic Arts in XP.

You should see two files, one with a .backup name. Delete the other file. Rename the .backup file to .sims3, removing .backup in the filename.

Ex. 

Sunset Valley.sims3 (bad file)
Sunset Valley.sims3.backup (good backup file) (rename it to Sunset Valley.sims3)

Start up The Sims 3, your saved file will now load.