The game will start at the beginning if you accidentally click on the Delete button, or if the savegame file becomes corrupted due to some sort of "bad" thing happening on your computer while the game is running. If you are running the Windows version, there is, unfortunately, no automatic backup of the savegame file. The Mac version of the game automatically creates a backup of the savegame file. If you would tell me which version of the game you are playing, I will work with you to see if your game can be recovered.