This is the first time it has happened. So I'm afraid I can't really help... Sorry. Are you sure you picked a save slot and saved it there, instead of just clicking save and then exiting the menu?
Yes, because I had two save files. one that was near the very beginning and one where the rats were at. i was around level 7 when it stopped working and my saves were gone.
I'm super sorry about the loss of the save files. I'm not really that savvy with this stuff, so I can't really help you with it. I tried to google for a fix, but I don't think anything I found would help.
