The Sims 4 White Screen CC Problem?

Hi @1800ToeMaster! Given that the unmerged files also didn't work and some of your CC does work, the next thing is to go through the CC you have and find the culprit or culprits -- which are most likely to be something you downloaded recently. Sims 3 CC, for example, can cause this. But it could also be a file that was broken but still around on the internet or that a recent patch broke. 

Unfortunately, there isn't a fast method for this. You'll need to do some version of a 50-50. This means organizing your files into bite-size batches and testing one batch at a time. For each test, delete the file called localthumbcache, then put only that batch in Mods. If your game opens, set that batch aside as "cleared" and delete localthumbcache again. If it doesn't open, take out half the batch and see if you're closer to finding the culprit. Remember to delete localthumbcache each time. You'll find some 50-50 method tutorials online too. Once you isolate the file, you can go find out if it was Sims 3 CC or if there's an updated version.

I'll just add that file merging doesn't help Sims 4 performance or make much difference to file size overall. 

And don't feel bad about ending up with Sims 3 CC or a broken file! I've been playing, with CC, for as long as that's been possible with Sims, and I still recently did that!