help gmod pink and black checker whole screen

When my son tries to play gmode the whole screen is black and pink checkers but you can still hear yourself shooting your gun. You cant see anything! What do I do? I never play gmod so please give me the dummy version . lol Thanks!
Shayne

Here are your options:

  1. In game, press Q and click Post Processing tab. Uncheck every checkbox you can find there, in every category on the left.
  2. Unmount Portal 2 and L4D2 ( Main menu > Controller icon in bottom right corner > Uncheck checkboxes near said titles )
  3. Verify integrity of game cache ( In Steam, right click on GMod > Properties > Local Files tab )

Or you can mount games that Garry’s mod is heavily relied on such as counter strike source and the half life 2 episodes.

Not those kind of missing textures.