Running help.

[Nig 13]

Be glad I actually took the courtesy of fixing this, 'cause somehow, I felt a bit bad for you:

onClipEvent (load) {
    var speed:Number = 0;
    var walk:Number = 6;
    var run:Number = 11;
    var grav:Number = 0;
    var falling:Number = 0;
    var jumped:Boolean = false;
    var jumpHeight:Number = 21;
    var touchingGround:Boolean = false;
    var scale:Number = _xscale;
    var doorOpened:Boolean = false;
    var attacked:Boolean = false;
}
onClipEvent (enterFrame) {
    if (!touchingGround) {
        grav++;
        this._y += grav;
    } else {
        grav = 0;
    }
    if (_root.ground.hitTest(_x, _y, true)) {
        touchingGround = true;
    } else {
        touchingGround = false;
    }
    if (!attacked) {
        if (Key.isDown(Key.LEFT)) {
            _x -= speed;
            if(speed == walk){
                this.gotoAndStop(2);
            } else {
                this.gotoAndStop(5); // running animation
            }
            _xscale = -scale;
        }
        if (Key.isDown(Key.RIGHT)) {
            _x += speed;
            if(speed == walk){
                this.gotoAndStop(2);
            } else {
                this.gotoAndStop(5); // running animation
            }
            _xscale = +scale;
        }
        if (Key.isDown(Key.SHIFT)) {
            speed = run;
        } else {
            speed = walk;
        }
    }
}
onClipEvent (enterFrame) {
    if (!attacked) {
        if (jumped) {
            falling += 0.5;
            _y += falling;
            if (touchingGround) {
                jumped = false;
            }
        } else {
            if (Key.isDown(Key.UP)) {
                jumped = true;
                falling = -jumpHeight;
                this.gotoAndStop(3);
            }
        }
    }
    if ((Key.isDown(Key.UP)) and (Key.isDown(Key.LEFT))) {
        this.gotoAndStop(3);
    }
    if ((Key.isDown(Key.UP)) and (Key.isDown(Key.RIGHT))) {
        this.gotoAndStop(3);
    }
    if ((!Key.isDown(Key.UP)) and (!touchingGround)) {
        this.gotoAndStop(3);
    } else if ((Key.isDown(Key.UP)) and (!touchingGround)) {
        this.gotoAndStop(3);
    }
    if ((_currentframe == 3) and (touchingGround)) {
        gotoAndStop(1);
    }
}
onClipEvent (keyUp) {
    if (!attacked) {
        gotoAndStop(1);
    }
}
onClipEvent (enterFrame) {
    if ((this.hitTest(_root.door)) and (!doorOpened)) {
        this._x -= speed;
    }
    if ((this.hitTest(_root.door)) and (Key.isDown(Key.SPACE)) and (_root.keys>=1)) {
        _root.door.gotoAndStop(2);
        doorOpened = true;
        _root.keys -= 1;
    }
    if (this.hitTest(_root.wall)) {
        this._x -= speed;
    }
    if (this.hitTest(_root.key)) {
        _root.keys += 1;
        unloadMovie(_root.key);
    }
    if (_root.keys<0) {
        _root.keys = 0;
    }
}
onClipEvent (enterFrame) {
    if (Key.isDown(65)){
        attacked = true;
        this.gotoAndStop(4);
        if(this.hitTest(_root.enemy)) {
            _root.enemy.unloadMovie();
        }
    } else {
        attacked = false;
    }
}

Frame 5 is for the running animation, just add another frame inside your movieclip on Frame 5 with the running and hopefully it should work