If you're on desktop, check that your save files are in the folder (check readme.txt for their locations.) If they are there,
1. Make a backup of all of your saves, and note their numbers.
2. Open up the game and make a save in every number slot that you have save files for.
3. Close the game, then replace those save files you just made with your backup saves.
After that, your save files should be usable again.