Flash video and audio problems

[lilicey]

I have a school project that needs to be done next week, and im bumping into a lot of problems in flash!

- I have a FLV video in my scene and when i go to another frame, it keeps playing. and when i come back to that frame, the video plays again (so there are 2 videos playing!). How can i stop the video from playing?
i tried to make a empty frame with no video and im using this code

import flash.events.MouseEvent;

    var music4:Sound = new Sound(new URLRequest("busy_bar.mp3"));
    var sc6:SoundChannel = music4.play(0, int.MAX_VALUE);

    deTrap.addEventListener(MouseEvent.CLICK, deTrapClick)

    function deTrapClick (evt:MouseEvent)
    {
    gotoAndPlay(35);
    sc6.stop();
    tv.gotoAndStop(6);
    }

    thePaper.addEventListener(MouseEvent.CLICK, dePaper)


    function dePaper(evt:MouseEvent)
    {
    gotoAndPlay(10);
    sc6.stop();
    tv.gotoAndStop(6);
    }

but I keep getting this error:

TypeError: Error #1009: Cannot access a property or method of a null object reference.
    at entrance_fla::MainTimeline/dePaper()

- My other problem is with the sound
Im now using external mp3's to play my sound (so the mp3's are in the same map as my swf)
but i want to use internal so i dont have to have the mp3's within the same place as my swf.
i tried to put the sounds in my timeline, but then i get the same problem with the video(it plays in the next frame)
im using this code for the sound:

import flash.events.MouseEvent;

    stop();
    var music1:Sound = new Sound(new URLRequest("city_ambience.mp3"));
    var music3:Sound = new Sound(new URLRequest("helicopter_flyby.mp3"));
    var sc2:SoundChannel = music1.play(0, int.MAX_VALUE);
    var sc3:SoundChannel = music3.play(0, int.MAX_VALUE);

    DoorOpen.addEventListener(MouseEvent.CLICK, DoorClick)

    function DoorClick (evt:MouseEvent)
    {
    gotoAndPlay(20);
    sc2.stop();
    sc3.stop();
    }

i really need help with this!
thanks in advance!