How can I use the audio of a video on a layer while showing another layer?

I have a video of myself explaining something. I placed the video on a layer, but cannot keep the audio of the video when I transfer to another layer to show some graphics. When I transfer to another layer, the audio of the video on the other layer gets cancelled. I want to be able to go back to my video presentation and back again to the layers with graphics while keeping the audio of the video presentation. How can I do that if it can be done in ManyCam?