i have never crossed this before - a video with audio video clip have triangles on the upper right hand side (on both audio and video). as a result, i can not apply a video transition over the video overlaying the end of hte one video onto the next. (the transition will work if it is ONLY on the end of the first of the two video. I have tried searching for this reason (or the cause of the triangle) without success. any help is appreciated.
You do not have the necessary Handles on your Video Clip. In Help, or the Manual (PDF), read up on "Handles." There is a lot of material there, but it's very important to understand Handles. Basically, what you will have to do is reset your In and Out Points to allow for the use of the Transitions.
a video with audio video clip have triangles on the upper right hand side (on both audio and video).
That means you are at the end of the clip. There is no more media past that.