are you using windows7? i was having the same problem until i realized what i was doing wrong.
when you click on the "desktop & displays" area, there will be a picture of your tv or monitor in the lower left corner of the screen with a small triangle on it. you either have to click the triangle, or right-click the triangle, and a little submenu pops up that says "configure"...click that and it brings you to the expanded menu for overscan/underscan.
i was thrown off on this at first because i was used to the windows XP CCC, but the CCC for windows7 is different. hopefully this helps if this was what you were experiencing