I just did some research, and apparently there's a program on Windows that will automatically shut your game down. Have you tried doing this:
1.) Go to your Documents/Sims 3 folder. Open one of the files that begins with xcpt in either WordPad or a similar program.
2.) Scroll down to the [exception info] section. If it says unknown module next to "address", then it was the Windows program that shut your game down. If it does not, check another of the files if you have any. If none of them say "unknown module", then something else caused the shut down and I'm not sure how to help you there.
3.) If it was indeed the Windows program that did it, open up your control panel, go to System and Security -> System -> Advanced system settings...