I've had Sony Vegas Movie Studio Platinum 8.0 installed for a week, and already know a lot of the ins and outs since I had a trial version before I bought it. However, an issue can cropped up, and I have no idea how to solve it.

Sometimes when I drag a video (that has sound) onto the bar, the video line appears, but not the audio line, and so the clip then has no sound. It does this on some, but not others, but I can see no clear difference between the clips. Plus, last week, I used the same clips without missing sound.

Have I accidentally hit a shortcut key that removes added audio? Please help.