I've bee having the same issues as everyone else. I've had some luck. I repaired the game after I moved my saves into a different folder and then played one of my older saves. I was able to play for a few hours (did not exit when I went to sleep), was even able to move my new family into a different lot. It was when I tried to explore the tree and go into a hidden lot that it finally happened again for me. I think it must happen when you try to move between lots or move sims or play different lots.
I can totally understand how frustrating it is especially if you just got the game for Christmas. I've had it since it came out so its not as big of a deal for me, I've been able to play it. I just hope it's fixed because the way I play I don't just play one lot, I wanna be able to play different houses.
Hope it gets fixed soon.
Oh and btw- I've done all the steps people have suggested, repairing the game, using one of the auto saves, uninstall & reinstall, running as administrator, etc. The only thing that seems to work right now, if you need to play it is by just moving your saves and starting fresh. Just don't move your family.
