The problem with Sony Vegas Pro 8.0 is that the preview screen is black, empty, however I do hear sounds. The video clip isn't muted.
The clip is in avi. format.

Sony Vegas doesn't accept .avi format, it only let's you hear the audio from it.
It's irritating, I know.

Just convert the .avi to and .mpg or something, then import it and edit it.

I have tried google but only found crappy trial converters.

Do you have a good free one?