I have a game called Tom Clancy’s Ghost Recon. I’ve had it for about a week, and it has run fine until yestarday. The game won’t cover the whole monitor. THe viewing area is in the center and then the rest of the monitor is black. I haven’t changed any of the settings. I cannot figure out how to get it back to the regular size. I’ve reinstalled it and tried changing the resolution. I’m running on windows XP.
This may or may not help… depending on your display drivers
right-click the desktop and select properties
click the settings tab then ‘advanced’
look for a ‘displays’ tab or equivelent
click your monitor and look for a “scale image to screen size” setting.
Yours is probably different but if you poke around hopefully you can find a similar setting.
good luck 
Try updating your display card’s drivers. If you have the newest driver version you could go back to an older version and see if that helps.
As a side note some people with illegal copy of the GR are experiencing screen size problems, but this of course doesn’t need to apply to you.
Have you installed any programs or changed any system settings?