If you uninstall the editor, maybe not everything gehts deinstalled.
I have a file 'DockPanel.config' (letter case does not matter in a Windows file system) in the directory 'Steam\SteamApps\common\The Divinity Engine Enhanced Edition'. Maybe it does not get uninstalled when you uninstall the editor and when you reinstall it, it's still there. If this file got corrupted somehow and why ever, there's a good chance the editor will no longer start, even after a reinstall.
A lot of programs leave changed files or files that don't exist in the original installation untouched if you deinstall the program, and this might have been the case for the Divinity Engine too.
Maybe this helps, other than this, I have no advice.
