Why doesn’t my video on sony vegas render correctly?

i’ve clicked with make film and render as ive tried plenty of formats but once i render it instead of the 6-7min vid i created the item some haphazard 21 second blank screen
– i am new on it and also its over a trial until finally it buy it for real sunday
-am when i clicking the wrong button
-wrong settings

not for you to sure concerning this but test moving that time-line pointer to the starting point of that video prior to rendering.