No video playback on extrenal monitor

Using FCP7 on OS 10.6.8 with Intel Mac desktop. I cannot get full video playback from FCP7 to an external monitor using a FireWire interface through a Canopus ADVC110 converter with S-Video out to the external monitor. I can get still frames to display, but motion video doesn't happen. It seems as all prefs/etc. are good as there is a still displayed, and it does change when timeline video is advanced. Pls advise asap. Thank you so much .Cheers!