If you check the '..\SteamApps\common\Divinity Original Sin Enhanced Edition; install folder, are the game files there? If so, can you start the game directly from the '..\Shipping\EoCApp.exe' program file, by right clicking and running as administrator?
Try logging out of Steam, exit the client, reboot, start Steam again, log in, and see if that helps.
Try checking your drive for errors. In Windows Explorer, right click the drive and select Properties, switch to the Tools tab and click Check Now in the Error-checking section.
Try exiting out of the Steam client, then browse to the SteamApps folder where the game is being installed and delete the contents of the 'downloading' folder. Right click on the Steam shortcut and run it as administrator and try updating/installing the game again.
