I recall something similar in setting up my CV3D. When I first installed the driver, the system would not boot straight up. On a native screen there was a requester asking what my monitor's default capabilities were - VGA, NTSC, or PAL, I think. Once I clicked something and defined some screen modes, the problem disappeared.
So:
Check the native output on a 15KHz monitor.
Make sure the CVision3D monitor driver has an icon - mine didn't by default, and that was causing some problems.
Check the Passthrough ENV variables.
Make sure there are some screenmodes defined in CGXMode.
Hope this helps!
