Do you know what your previous resolution was?  You can edit the Game.prefs file to go back to your former resolution by editing it in notepad.

It isn't too complicated, you just have to open Game.prefs in notepad (you will find it in your My Documents\My Games\Gas Powered Games\Demigod folder).  Once you have it open go to edit > find and then in the prompt search for 'primary_adapter' (without the quotes) and press find next.  The first thing that comes up should be your resolution settings.  Your screen width is the first number, the height the second number.  Just change those two to what you were using before and save the file (make a copy first if you are worried) and try starting the game.