In the future, you will want to try to get away from the actual on button code.

Give you button (or MC) an instance name, then from the main timeline or a separate .as file, you will switch to something like this:

[code]
myBtn.onPress = function(){
this._parent.gotoAndPlay("over");
}

The correct syntax for "this._parent" will vary depending on where you place the MC/button. it could be this._parent._parent, or whatever...

best way to know.. find the cross hair icon in the actions pane. click it. Find the reference you want (the button, in this case) and click it once. The syntax will appear in the top of the window there.

Yes, you can use "_root" but remember, we are now on Flash 10, and 11 is coming. _root, is out as of AS3, and depreciated in AS2. Get used to not using it. it will break things in the future.