just thought i'd share a fix for how I FINALLY got around the black screen issue, as I have seen many others have had the same issue as me and are looking for here for help, although the fix is not a great one..
you need to go into Library>Application Support>Telltale Games>
here you will find where the game stores your saves in the folder "TheWalkingDead"
you will need to remove this folder from where it is, I just dragged it out onto the desktop as to not delete my saves.
Now start up your steam version of walking dead, you will find that all your save games are gone, but if you begin a new game from the beginning of episode 2, the game should run fine, at least it did for me.
Note: you will lose all your progress and choices you made from your last game as the game now creates these randomly, but hey at least we can finally play the game now, weeks after release. So if you are sick of sitting around waiting for TTG to pull their finger out of their ass and release a fix/patch for it, this may be a solution for you, hope it helps :)