Xfx radeon 5870 and 24 monitor

When i installed my 6850 i had black boarders around the screen image and your problem sounds similar.

I had to adjusted the scaling options in catalyst control center to make the display fit the screen.

Make sure you have have up to date drivers then go to CCC -> My Digital Flat-Panels -> Scaling Options -> and set to 0% (Overscan).

Hope that works.

Good Man GreyMachine it works !!! Thanks very much