I had that problem as well with Win7 after a fresh install.
If you are using a Nvidia grafix card that will be the problem.
Stay away from the latest official driver (191.07), get the beta driver (195.39) from
http://www.nvidia.co.uk/Download/Find.aspx?lang=en-uk
That did the trick for me!
Other thing you could try..
Do a fresh Win7 install.
Install DFO and let it update.
Install the drivers one by one, and start DFO after every install to check if it works.
If DFO won't start after a specific driver, try an older version or a beta.
Good luck.