How is your external monitor hooked up to FCP? Through the camera?
If so, first ensure that your Audio Video Settings are set to send out audio and video via Firewire. Also ensure that your output settings are correct. That is, if you’re editing HDV, make sure you’re sending an HDV signal back out to the camera. If you’re sending the wrong signal back out to the camera, it most likely would not show an image.
Lastly, ensure that your camera is set up correctly to pass the video through to the monitor.
Walter Biscardi, Jr.
Creative Genius, Biscardi Creative Media
https://www.biscardicreative.com
Now in Production, “The Rough Cut,” https://www.theroughcutmovie.com
“I reject your reality and substitute my own!” – Adam Savage, Mythbusters