Should have a program in the Prefs drawer called
"CGraphX Mode" after a fresh install. Just go in
there and select the applicable screen mode you
may need to build a specific KHz driver and put
it in your devs/monitors drawer (on some monitors).
Also check your "Screen Mode" preferences and see
what they are set at. It's tough to guess your
problem without knowing what kind of monitor and
what version of CGFX.