I'm sorry you are still experiencing this problem.
This is a bit extreme, but please try removing all Walking Dead game data, including your saves (you can try backing these files up in another directory to avoid losing your progress). Your saves are located in Documents\Telltale Games\The Walking Dead. Please delete or remove this folder in its entirety. Also make sure there are no lingering files in steamapps\common\the walking dead sub-directory in your Steam folder.
Once this is done, uninstall and then reinstall Steam. Now try reinstalling The Walking Dead (but do not move your saves back just yet). Once installed, try to run the game. If the game now works, please close the game and try moving your saves back. If you again expereince the issue where the game will not run, then it's more than likely that your prefs file is corrupted, and can no longer be accessed. Unfortunately this means your saves cannot be accessed either.
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