I hate to say it, but sometimes the game just crashes to the desktop for no reason. It's just the nature of the beast. I suggest you get into the habit of saving frequently. A lot of players save every Sim day, usually when they are sleeping. Of course, that doesn't help if it crashes in the middle of building a house.
I attest to that, and can't emphasize it enough. I save whenever I think about it...sometimes as often as every five real-life minutes. I always save right after I've done something major, such as add something to the house, or analyze a bunch of relics and then placed them(I have them in a certain order, just like all my gems and stuff...I think I'm borderline OCD with some things, but it ends up looking very nice due my perfectionism...you should see my gem display).
Anyway, I've had the game freeze up, but when it does, I can still see the current Sim's plumbob moving, so I just sit it out. Thus far, it always resumes after less than a minute, possibly a minute, but never much more than that. Ack. It seems unfair, since my computer is way above the minimum requirements. We're talking 3GB of RAM, and an NVidia GeForce 9800GTX+, which, at the time my computer was upgraded, the best I could get(since it's a prebuilt). On the other hand, I read, even here I think, that the game is hardcoded to only use a maximum of 2GB of RAM. Why? It can be a CPU hog, especially when there are Sims everywhere...why would EA do that? It makes no sense. Especially when you think about 64-bit systems, that have crazy amounts of RAM(although, I know nothing about 64-bit systems, so maybe that extra RAM is used for something else?)
BTW, have you tried backing up your saved game to a safe place, uninstalling, deleting all the TS3 folders from the Documents/My Documents folders, then reinstalling? I fixed a major problem with my 'prize' savegame that way.
