gap around picture

There is about a 2 inch black gap around the picture on tv screen. ive tried adjusting the screen calibration in the skin settings but it is already set to 1920x1080 which my tv is. is there a way of fixing this or am i stuck with it. it all seemed fine when i had a 720 tv.

thanks for the advice and quick reply. your advice worked, tho mine was nvidia not ati.
Problem sorted. thanks for the help