Ruby, the save game file might be too big for your computer to run at once. Every computer is set up to run/use only a set amount of RAM and if the game file is bigger than the allowed amount, crashes happen all the time. Find your latest crash file (called
xcpt[something].txt), it should be in the Sims 3 folder where you find your saves/screenshots/download folders. I usually find mine listed at the very bottom and they are dated and timed. Doubled click to open and find the line about
Free Virtual Memory, if it is
less than 200Mb then this could be your problem. My husband and I found
this Sims Wiki page that helped us fix my Dynasty file so I could continue playing it! It talks about downloading an application -
this is not a game mod - that allows you to increase the amount of RAM designated to your game when you're playing it.
My husband could probably walk you/us through it if this is the problem and you need help. Let me know what you find out.