Hello Fennster buddy!, So as you're aware I tried to help you via steam but now I know what has happened. Here is a few tips:

Verifiy TF2 Cache
Delete Unwanted Adons System 32 > Steam >Steam Apps>Common>Gary's Mod>Gary's Mod>Addons

If none of that helps you, I suggest you support a ticket.
support.facepunchstudios.com/ticket/34545