I also have a trial copy on my laptop. I can view the video preview and can hear the audio too. I have compaired every setting that I can find, but, still no video.
Maybe you changed the opacity of the track. Hover your mouse over the lower edge of the video track. Does it change to a hand, a tool-tip will appear stating the opacity level. If it says "Opacity 0%", drag the blue line up to 100%. Actually it's the video event not the track that gets changed, but you get my point.
However, if you hover at the top edge of the video track and it already says 100%, your problem is something else.