CSS Models won't work, maps won't load

I’m not one of those people that just downloaded all the textures and models of counter strike so certain addons would work, I actually purchased the game. All the stuff is in my inventory, but when I spawn them, nothing happens. Whenever I try to launch a CSS map it closes the map screen and returns me to the main menu. I am a Mac user, while my brother is PC and having the same problem. Please, I have reinstalled Garry’s Mod and it has done nothing.