Start a save in Sunset Valley for example to check. It's best to reinstall in small batches of say 5 files at a time. – If the tools above don't work: You can also go through your mods/custom content a few files at a time, specially if you're seeing a lot of faulty files when using the tools. May show false-positive corrupt files (the red/orange highlighted files.)
You can remove any bad or corrupt files and resave it. – Custard Sims3Pack Cleaner: ( ) This tool helps look at what's inside a single Sims3pack file. To make sure you know everything is good. That's why it's recommended to do a manual check of your mods and custom content. It may also false-flag files, making them look like they're bad when they aren't. Please understand, It will show conflicts between some files, but not all. There is a couple of tools to check mods/custom content. This might be true for ModtheSims as well. If you are a member of Sims Resource allow you to look at your downloads history and download many files at once, I believe. The CC may need to be gone through and tested beforehand. – For Info: Be careful finding and downloading zipped custom content folders from Sims 3 youtubers, tumblr sites, etc.
