So the DLC was acting stranger for some reason. It wouldn't let save even though it says it’s saving, it always started at Vince’s story no matter what I did, and when I want to the main menu from Vince’s story, the screen of the game got smaller and one of the files disappeared (only to reappear when I restarted the game).
So (after trying many, many things) I asked people for help and they said that I should uninstall 400 days and then reinstall it again. They said that I should delete WalkingDead106, and if I did that then Steam would allow me to reinstall 400 days. I was a bit wary of doing that, but I eventually did it anyways.
The problem is, the game and Steam still says that I have the 400 days DLC. But when I try to play the game, the screen goes black and I'm forced to shut down my laptop. The rest of the game works fine, it's only 400 days that's the problem.
Is there a way for me to make the game/Steam know that I don't have 400 days anymore so I can reinstall it back onto my computer?