Ok, I have the exact same propblem here. Windows 8.1, 2600K, 7990 GPU.
Never played the game until trying today and...nothing. Just black screen, cursor and nothing happens.
I have tried the replacement D:OS folder in My Docs, no go. I have tried changing my screen res, no go.
In the Event Viewer, I am given the following:
EoCApp.exe
1.0.252.0
1114
01d0e95d391222a2
17
F:\Steam\steamapps\common\Divinity - Original Sin\Shipping\EoCApp.exe
a4a4a4ca-5550-11e5-82c7-902b34322e00
55006E006B006E006F0077006E0000000000