Hello jessjed,
You could try the following:
- "Find the sims 3 saves folder usually in Documents/Electronic Arts/ The Sims 3/ Saves. Find the most recent sims3file.
- Then find the one that is a sims3.backup file.
- Change the name of the most recent one to Sunset Valley.sims3.bad and then rename the backup to Sunset Valley.sims3 (no period after sims3).
- Whenever you play the game make sure to use "save as" (just number them, 1, 2, 3 etc) instead of save and be sure to save often.
If this still doesn't work, then you'll probably have to do a clean install. Do you have any mods or CC installed?