Half-life video mode prob

I got a new computer with the radeon 9800 pro in it and when i try to run half-life in opengl mode i get a box in the upper left hand corner with the main menu while i play. the other video modes work fine, but i like to run in opengl. i ran half-life in opengl on my old computer and never had this problem. i was wondering if it was a problem with the new video card? does anyone have a fix for this? thanks.