Monitor help please ?? !! ?

I have an LG 23" glossy 1920 X 1080p, A Core i7 + 8 GB RAM + ATI 5850 Radeon GPU which I have been using with a standard VGA/DSub hookup. I was getting some screen rippling effect on games (especially on darkened screen areas) so I ordered a DVI/HDMI cable to use instead. It appears to have solved the rippling issue, but now my whole desktop had squeezed in almost an inch on both sides, and a 1/2 inch on top and bottom. In other words, it is not using my entire monitor screen like it was before. How do I get the who screen back? Monitor resolution seems to be set at max 1920 x 1080