Are you shutting down all non-essential programs (especially anti-virus) before trying to start the game?
Try verifying local files: in the Steam library, right click on the game and select Properties, switch to the Local Files tab and then click on the 'Verify Integrity of Game Cache...' button.
Try exiting out of the Steam client, and starting the game directly from the '..\SteamApps\common\beyond_divinity\div.exe' program file, by right clicking and running as administrator.
Right click the executable, select Properties, switch to the Compatibility tab, and set it to run in a compatibility mode (Win9x, or XP, etc). You can also set it to always run as administrator, and 'disable display scaling on high DPI settings'.
Try the
4GB Patch to increase the amount of virtual memory that the game (or any 32 bit application) can access in 64 bit versions of Windows.
