problem in creating a maza game by drowing line

hi

i've created a maze game

the idea is to solve the maze by drowing a line

and its works fine as long as i didn't use any thing as a background.

the code

stop();

  import flash.display.Sprite;

  import flash.events.MouseEvent;

  var drawing:Boolean;

  var isStart = false;

  graphics.lineStyle(3,0x000000);

  drawing = false;//to start with

  stage.addEventListener(MouseEvent.MOUSE_DOWN, startDrawing);

  stage.addEventListener(MouseEvent.MOUSE_MOVE, draw);

  stage.addEventListener(MouseEvent.MOUSE_UP, stopDrawing);

  function startDrawing(event:MouseEvent):void{

  graphics.moveTo( mouseX, mouseY);

  drawing = true;

  }

  function draw(event:MouseEvent){

  if(drawing){

  graphics.lineTo(mouseX,mouseY);

  }

  }

  function stopDrawing(event:MouseEvent){

  drawing = false;

  }

stage.addEventListener(MouseEvent.MOUSE_MOVE, detectHits);

function detectHits(event:MouseEvent) {

if (wall_mc.hitTestPoint(mouseX,mouseY,true)) {

  if (isStart == true) {

  graphics.clear();

gotoAndPlay(3);

  isStart = false ;

stage.removeEventListener(MouseEvent.MOUSE_MOVE, detectHits);

  }

}

else if (hit_mc.hitTestPoint(mouseX,mouseY,true)) {

  if (isStart == true) {

  graphics.clear();

  gotoAndPlay(2);

  isStart = false ;

stage.removeEventListener(MouseEvent.MOUSE_MOVE, detectHits);

  }

}

}

mc_start.addEventListener(MouseEvent.MOUSE_OVER, fl_MouseClickHandler);

function fl_MouseClickHandler(event:MouseEvent):void

{

isStart = true ;

}

i need to set a background to this game

but when i do the lines never drew