Are you shutting down all non-essential programs (especially anti-virus) before starting the game?
Try starting the game directly from the '..\SteamApps\common\Divinity - Original Sin\Shipping\EoCApp.exe' program file. Perhaps right click and run as administrator.
Did you try verifying local files? The re-install should have fixed any missing or corrupt files, though.
These were probably in the support email, but:
Did you check for driver updates, etc?
If you start dxdiag (click Start or WinKey-R, type in dxdiag and hit Enter), does your sound device show up with the name and drivers?
Uninstalling AMD Gaming evolved (raptr) software has fixed startup crashing for some people.
Check if the support packages for the game are installed correctly (in ..\steamapps\common\Divinity - Original Sin\_CommonRedist).
