Bounce and randome velocity

programming flash
1

Hi everyone,
I am trying to make a simple game with a bouncing movie clip. the function is initialized else where. I have hit a few road blocks and i cannot seem to get the item to: go in random directions or bounce when it reaches the sides of the stage.

I think i need to incorperate another vector into the movement but im not sure how.

All help is welcome!
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var radius:Number =10;
var vx:Number = (Math.random()*8-4);
var vy:Number = (Math.random()*8-4);
var bounce:Number = -1;

function onLoop(event:Event):void {
spermA.x += vx;
spermA.y += vy;
var _vx = spermA.x + vx;
var _vy = spermA.y + vy;

if (spermA.x + spermA.radius > stage.stageWidth) {
    spermA.x = stage.stageWidth - radius;
    _vx *= bounce;
    trace(sperm.A.x);
} else if (spermA.x - radius < 0) {
    spermA.x = radius;
    _vx *= bounce;
}
if (spermA.y + spermA.radius > stage.stageHeight) {
    spermA.y = stage.stageHeight - radius;
    _vy *= bounce;
} else if (spermA.y - radius < 0) {
    spermA.y = radius;
    _vy *= bounce;
}

}

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Thanks!