Larian Studios Forums Divinity - Original Sin Divinity - Original Sin - Technical Issues Crash on startup [Solved]

Try renaming your current '..\My Documents\Divinity Original Sin' folder, and replace it with the downloaded version.
If that lets you start the game, then if you have saves in your existing profile, you can just move them from the renamed folder to the savegames folder for the downloaded profile (or create another new profile).