I have downloaded Vegas HD 10 but the trial works for a while then comes up with a notice saying its stopped working. Do I need to upgrade my graphics card please?

Every time I open up the programme to edit the Movie a notice keeps coming up saying Sony Vegas has stopped working, then crashes by exiting the programme all together. Also I keep getting blank green squares on the time line where there is audio only, but no picture. I'm not buying it if the trial itself, if it keeps crashing, otherwise this would have been a good programme.