Try using Alt-F4 to exit out of the game.
Check for updated graphics drivers and Windows updates (especially anything DirectX related).
In the '..\SteamApps\common\divinity2_dev_cut\bin' folder, try right clicking an executable ( Divinity2.exe is the normal mode, while Divinity2-debug.exe has the optional 'Developer Mode' cheat menu), select properties, switch to the Compatibility tab and try different compatibility modes (and maybe check the option to run as administrator, and disable display scaling on high DPI settings).
You can try setting the game to run in a window, by editing the file below in a text editor and changing the one to a zero in Fullscreen="1".
C:\Users\<UserName>\AppData\Local\Divinity 2\Profile\graphicoptions.xml
You may need to set Windows Explorer to show hidden files and folders:
http://www.howtogeek.com/howto/windows-vista/show-hidden-files-and-folders-in-windows-vista/(covers Vista through Win 10)
Alternately, I've see the
Windows Borderless Gaming app reported to work with Divinity 2.
