Are you shutting down all non-essential programs (especially anti-virus) before starting the game?
Try exiting out of the Steam client, and starting the game directly from the '..\SteamApps\common\Divinity Original Sin 2\bin\EoCApp.exe' program file, by right clicking and running as administrator.
Try browsing to the '..\Documents\Larian Studios' folder and manually create the 'Divinity Original Sin 2' subfolder.
This folder contains the saved games, configuration files and a level cache folder.
Next, extract the replacement folder from the download below into your '..\Documents\Larian Studios' folder. That should let you start the game, and then you can see if you can start a new game and save/load, or create a new profile.
https://www.dropbox.com/s/kjvq79igruaeu4h/DOS2_doc_20165341.zip?dl=1The graphicSettings.lsx file is set to 1280x720 Windowed mode, Very Low quality preset, which you can change in the options (manually, or hit autodetect).
If that doesn't help, you can delete the downloaded My Documents D:OS 2 folder.
Try creating a new Windows administrator user account, switch to that account and try starting the game from there, directly from the executable.
Try doing a clean boot and then test the game. Click Start, or hit WinKey-R, type in msconfig and hit enter; in the General tab, click Selective Startup, uncheck Load startup items (if required) and leave Load system services and Use original boot configuration options checked. Next, Click on the Services tab, check the box to Hide all Microsoft services, then click the Disable All button (maybe make a note of which are currently enabled/disabled), then click OK and reboot the computer.
Run msconfig again to switch back to the normal boot configuration.