If you don't see any video in the main window, right-click (or ctrl+click with a one-button mouse) in the middle of the main window to get the Flash context menu. Choose "Settings..." from the menu, and then click the "Camera" tab (looks like this). Try choosing a different camera from the list. If you click the small box just below the list you can test the camera. When you find a camera that lets you see video in the box, click the Close button on the camera settings window.

Close this window