I downloaded a few custom houses for the first time recently (and I'm not sure if it was after this or a different modding session) and my game has stopped responding on startup now. When I start it, all I get is a black screen. For the course of the day I have been able to close out of the game, start it up, and hope for the best that it loads, but now it won't start at all, and I can't even install any new mods because when I hit 'Install', I get a black loading screen as well. I think it might have to do with some of the houses that I downloaded, but a few of them are already in a town. I doubt there is anyone living in them yet, but I'm not sure what will happen if I uninstall them. I don't want to jack up my neighborhood anymore than it already is, ya know?

Have you tried the steps in this guide? Game Help:Sims 3 Game Problem^wiki Simply test (without saving) to see if any of the steps help or solve the issue.