Hi Kaykay,
Does your game give you some kind of error message? Having this info would be helpful as it helps us search for a solution.
If it doesn't give you an actual error message try one or all of these tips.
Factory Reset:
01.) Go to your Sims 3 folder.
-- Documents > Electronic Arts > The Sims 3
02.) Rename your current Sims 3 folder to something like Sims 3 Current.
03.) Click the Sims 3 icon to create a new The Sims 3 folder.
04.) Then copy your game saves, files and such over to the new game to see if that helps.
How To: Saving folders/files to use on a different computer or to use as backup
http://www.carls-sims-3-guide.com/forum/index.php/topic,16414.msg313134.html#msg313134Restarting the computer maybe helpful as well.
Delete the cache files (socialCache.package, Sims3Logs.xml, simCompositorCache.package, scriptCache.package, compositorCache.package, CasPartCache.package)
If you've got custom content (Which is game content that is not provided by EA Games) Try starting the game without it, by going into the game options and checking start game without custom content.
If you have mods in your game. Try running the game without the mods. By moving the mods folder out of your Sims 3 folder. If you'd like to keep a copy of the folder, copy it to desktop or wherever you keep your backup Sims 3 files.
If you find that none of the above help, please post back so we maybe able to help further.
MrsFlynn