I'm going to error on the side that you've probably tried these tips, but just in case you haven't. Have you tried the following:
Delete the cache files (socialCache.package, Sims3Logs.xml, simCompositorCache.package, scriptCache.package, compositorCache.package, CasPartCache.package)
-- Also delete everything except Ccmerged.package file in your DCBackup folder.
-- Documents > Electronic Arts > The Sims 3 > DCBackup
04.) Check your active household's family and individual inventories, as having to many items (100 or more items) in their inventories may cause lag and freezing. This can happen fast if the sims is a fisher, gardener or alchemist, not to mention collector.
Factory reset - Copy your Sims 3 folder to the desktop. Rename your current Sims 3 folder to something like Sims 3 Current. Click the Sims 3 icon to create a new Sims 3 folder. Then copy your game saves, files and such over to the new game to see if that helps. (This is different from a total-game reinstall)
If you need to know what to save/backup. Have a look at this thread.
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#msg313134Run a register cleaner program. (Something like Ccleaner, It's free -
http://www.piriform.com/ccleaner/download)
This helps clean up temporary files, internet cache files and other files that are left behind that are no longer being used, after uninstalling.
Disk Cleanup and Defrag are helpful to do as well.
-- All Programs > Accessories > System Tools > Disk Clean Up
-- All Programs > Accessories > System Tools > Defragmenter
These paths were made with Windows 7 in mind. With Windows 8, they maybe different. These programs will help clean out the unnecessary and temporary files on your computer and reorganize your hard drive to make it run smoother.
And just to note, some of the expansions and towns are graphic intensive and take a lot of processing power of the computer. Pets, Supernatural Seasons, University Life, and especially Island Paradise. So you may want to take that into consideration.
Playing for long periods of time (2+ hours or more) without saving will cause lag and freezing too. So save often. I try to save at least every hour.
Anyway, I hope some of these tips will help,
MrsFlynn