I was having an issue with no video at all in full screen mode (switching to windowed mode helped - but I wanted full screen).
After reading this topic I was playing a bit with mentioned parameters and came to conclusion that this is somehow related to "aspect" parameter. When changed to "true" - problem dissapeared.

Hope this will help someone with similiar problem.

Thanks a lot, that solved my problem. I noted that when switching from full screen to windows, video would show so I knew that a simple query on GOG forum would solve the issue.

Ok, I have found out that when parameter "output" in the [sdl] section is changed from default "surface" to "opengl" - everything works fine in full screen :)

This topic is based on Windows 7 64 bit, and Core i5 integrated graphic card. (Dell Latitude 5220)