Below is the question I asked steam support and they suggested verifying the cache which does nothing:
I purchased The Walking dead and the first time I played it it had a few judders and freezes but generally worked without major disaster. However, I try to start the game the next day and every time it starts up the screen displays this 'corrupted texture' look and various parts of the image are jumbled up with black blocky areas in between. Something like a digital mosaic. Therefore I cannot see anything. However, I can here the game menus playing through my speaker and the menu is still active to interaction. Despite my best efforts of installing and reinstalling the issue continues to arise. Is there a solution to this bug, glitch or error?
Note: I am using a Macbook with Snow Leopard 10.6.8 OS X. The processor is a 2.4 GHz Intel Core 2 Duo.
Something else I should add is that steam show that the game has been played. So its clearly running its just covered up by this corrupted image. The game also opens in full screen so the toolbar at the top of the screen or the dock at the bottom can't be accessed. The only ways to exit the game once started is to press 'Esc' or reset the laptop.