No fullscreen.

Ok I am using a Quad Core, GTX 295 and run Windows 7. Whenever I start up crossfire, it starts like when you would put it in windowed mode, but then when I try to go in game it only takes up about 3/4's of my screen, it's really annoying and ask if anyone could find a solution to this. I have tried putting it in fullscreen, because it was set to windowed and yet it still does the same thing, if anyone would help, please do.