I am trying out Vegas 9.0 Pro. I have some content on the timeline and have burned a DVD by clicking on Tools->Burn Disc->DVD. But when I try to play the new DVD on a computer, there is no audio or video. My burner is TSSTcorp DVD+-RW on an ordinary Dell PC. I have tried DVD - as well as + blanks. I have varied the burn speed as the manual suggests. Is there a simple concept I am missing?