Similar things occured to myself when I'd recently installed the game a long while back. That was due to that I was always troubled by save error 13 and 12, which resulted in corrupt save files. The game keeps its own backup, so have you checked if you can use the save file second to last? I was able to play really long on backup systems before I solved my problems.
Save error 13 stopped for me for unknown reasons, and I think I mentioned in a nereby thread how to minimise the save error 12s.
PS. I always have testingcheatsenabled true going (almost never use it, but if I want to I wish it to be close at hand), and I do not believe that is the problem. It seems so much more stable than its equivalent in sims 2.