Sims 4 won't start. I get a loading circle, and then it goes back to Origin.

To check if it is CC or Mods related, move the contents of your Mods folder to the desktop (except resource.cfg).

If the game then works you just have to find out what CC/Mod causes it.

Now it doesn't do anything anymore... I can click the Sims as much as I want, but there's no reaction, not even a loading circle. 

Rightclick the game in Origin and select repair.

If that does not work gather a DxDiag and attach it to a post.

https://help.ea.com/en-us/help/pc/how-to-gather-dxdiag-information/

I have a DxDiag saved, how do I attach it?

Click on Browse just above the submit button.

Ah, right here. 

Your graphics is well below minimum requirements. It's a wonder you got it to work in the first place. Adding CC broke its back so to speak.

And deleting CC won't help? The computer just can't handle the game itself? 

(It worked fine, even with settings normal/high. I had quite a lot of CC already, and it never seemed like it was too much.) 

This has been happening to me for about a week and I've tried uninstalling it and taking out the mods and it still wont work, I've never had any problems with the game before and this happened suddenly. I'm sorry I cant help you fix your game!