some full screen games refuse to JUST set a resolution for the game itself, it forces the entire computers desktop to change to it also.
if you caused it to crash, just forced closed, or whatever; it didn't change itself back.
i played a game once that wouldn't let me use up to my 1920x1200, just a max of 1440x900.
yet the desktop changed itself down to 800x600 during this time. i will never understand it