It's most likely a corrupt sim, MissAldith. I have that problem from time to time, (and currently I still have a brown hair that's crashing my bodyshop and game when I scroll to the position it's in... not to mention a random corrupted teen sim that crashes the game whenever I click on it. :dontknow:)
You might want to try to completely pull your "SavedSims" folder and see what happens with that. This also goes for everyone else as an option, because a random corrupted sim can cause it to crash upon startup. If that doesn't do any good, there's always the possibility of a corrupted custom clothing/object mesh in your Downloads folder, whether old or new.
