Did you try the tips here: http://answers.ea.com/t5/The-Sims-3/FAQ-Lags-amp-Freezes/td-p/646/ ?
First thing to try is the cheat resetsim * to reset all Sims in your town.
I am unable to enter this when the game has frozen up, and using it beforehand has seem to have done nothing, as it freezes as soon as I go into live mode.
May have found a fix, in my case anyway. I uninstalled the base game, deleted all leftover files in the Program Files (x86)/Electronic Arts/The Sims 3 directory, uninstalled Seasons, reinstalled the base game, applied the 1.42 patch and reinstalled Seasons. So far so good, no freezing at all anywhere.
