Then always use the "save as" option when saving your game. Might I suggest that you do a Factory Reset, See the stickies in technical help. Why don't you put it down to a learning experience and start a new family? It's worked for me in the past:) Sadly, from what you say, I think you have peobably lost your sim. But, I don't think you need to panic about the games not working. I'm guessing it's got something to do with the University pack because it's only started doing it then, and everytime it does crash it's when my sim is either coming back from uni or is still there. It's really annoying especially if it's gonna keep happening again and again. I can't do anything and I really don't want to have to delete my sim again because I've spend ages on this game! It has her name and stuff at the bottom but when I try an click on the moods option it won't let me see it. I saved my game and left and when I turned it back on my sim doesn't exist anymore. I've tried the resetSim option again but it won't work, also my sims photo won't appear in the green box at the bottom left of the screen either. There was no option to click for "return sim to home" and when I clicked for her to move or do something she wouldn't do it and will just stand there forever. The last time it's happened my sim had just come back from university, and was struck on the hill just outside the town. Really annoying especially cause she was the 3rd generation in that family! My whole sim disappeared and I couldn't get her back, nor could I go back to her family house which was in the other neighborhood.
The first time it happened I logged on and my sim wouldn't get out of bed, I tried resetSim and it didn't work (I tried everything), eventually I had to delete my sim thinking it would then reset the sim but it didn't. This has happened twice before and I think it's because I've recently installed the University expansion pack.