Using Vegas Movie Studio to edit screenr screencasts

Hi everyone,
Seasons greetings .
I am trying to edit screenr videos on Vegas Movie Studio (add an intro / outro as well as captions ). The problem is that when loaded on Vegas, the preview screen shows blank but the audio will be working . When rendered, it shows a black screen. Other movies show perfectly well on vegas .Have you encountered this problem before?

All I want to do is to add the intro / outro , and then save it again as mp4 so that it can be viewed on cell phones .

Do you know any other software that can do this? Windows media player can do it but the quality is lower and it doesn't save as mp4.

Thanks in advance for your answers.
Reagrds,

Yvonne