So Windows is fine on the TV?

Can you start the game on a monitor, set the resolution to something your TV supports, and then switch to using the TV? You should be able to find a manual or something online listing the supported resolutions and refresh rates of your TV.

Even with the Steam version, AFAIK you should still be able to manually change the resolution. From the 'Crash to desktop' section of the PC DKS Support FAQ topic;

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Changing the resolution manually is done in this file:

Windows Vista and Windows 7: C:\Users\[WindowsUser]\AppData\Local\Divinity 2\Profile\graphicoptions.xml

Windows XP: C:\Documents And Settings\[WindowsUser]\Local Settings\Application Data\Divinity 2\Profile\graphicoptions.xml

Right-click and choose edit, or open it in Notepad or another text editor.

Change the following values and set them to a safe and low resolution, for example:

ScreenWidth="800" ScreenHeight="600"

Save the XML file and try to boot the game.

If that doesn't work, try to manually change these options in the same xml file:

UseHDR="0" UseDesktopResInFullscreen="0" ShadowTimeSlicing="1"

Save the XML file and try to boot the game.