you missed something in your thinking! :)
you're current code:
onClipEvent(enterFrame){
_x+=speed;
if(_x>300){
speed=0;
gotoAndPlay(9);
}
}
alright, _x > 300 and it gotoAndPlays(9), right? right.
but _x remains > 300 so it gotoAndPlays(9) on every new entering frame! ;)
I suggest using some kind of trigger variable. eg:
onClipEvent(load) {
triggered = false;
}
onClipEvent(enterFrame){
_x+=speed;
if(_x>300 && !triggered){
speed=0;
triggered = true;
gotoAndPlay(9);
}
}