You are not using a ChaseCam, or using a ChaseCam but don't have the TraqSync connected. The video displays a black screen.
If you are using a TraqCam cable, make sure that you are turning the ChaseCam PDR on before starting to record data. Otherwise the data/video gets out of sync and you might be recording your stay in the pits.
It may be possible that the amount of recorded video is less than the initial recorded Traqmate data (for example the time spent in the pits before an event). TraqStudio initially selects all complete laps so the first selected lap 'begins' after the end of the video. (remember the video and data still need to be synchronized).
On the driver dash, click 'Setup', and on the right side select 'All' to turn on all laps and the trips to and from the pits. Click the '|<<' button to move the position slider to the beginning of data (left most position). You should now see something in the video window. Use the Settings button on the Traqview Video Window to show the form for synchronizing the data and video.