I've been using the VSE for awhile now and have yet to encounter this problem.
I finished editing my video and clicked render animation. Everything seemed to be going fine. After the video finished rendering I went back through to watch the rendered video and it was just a black screen with no sound. Image overlays I had added to the video would still show up at the appropriate times, but no video or sound.
I tried reloading the file and restarting Blender, but neither of these things works. Can anyone give me any advice? It took me 3 hours to finish editing this video and now it's just gone.