Reactions to story from Video Editing Forums: Digital Director

Hi Everyone, I am working on a business video, with 5 interviewees. I started this project by creating a few seperate project files for each person. I now want to merge them. Copying and pasting is clearly not the way to go because it not only deletes all the transitions and title slides, but I suspect it is the reason for my bigger problem. The sound files exist until I close the files. When I return, the files seem to exist, but the soundwaves and audio have disappeared. I have tried copying the file to a new location using the Project Manager, while deleting all the Audio Conform and Preview files (I read that this might work on another forum, but it didn't).