Remove Movie Clip

Question

I would like to have the user click on a button or movie clip
that takes them to a new scene with multiple questions on it, and
depending on what answer they choose, come back to the main scene
and the button be gone, and replaced with a graphic (that won't
have any function). I thought I could change the alpha of the
graphic (sallylock_mc) from 0 to 100, but its only staying on 0.
And, I can't figure out how to make sally_mc disappear. So far,
here's what I have:
Main scene:
stop();
sallylock_mc._alpha=0
sally_mc.onRelease=function(){
_root.gotoAndPlay("sally");
"sally" scene:
stop();
sallyright_btn.onRelease=function(){
_root.gotoAndPlay("main");
sallylock_mc._alpha=100

Answer 1

OK :)
sally_mc (I changed it to a button, so now it will be
refrenced as sally_btn) exists in the very first frame of the first
scene ("main")of the movie. You have to click it to go to the scene
called "sally" Within the scene called "sally", there is a question
and answers. When the user clicks the right answer, I want them to
go back to the "main" scene, and I want sally_btn to be gone, and
replaced with what looks like a padlock, which I have called
sallylock_mc (it is a movie clip, don't know if it has to be or if
it should be something else.) Also, I want the padlock to only
exist/be visible on the "main" scene. I've found that when I go to
the other scenes, the padlock is there, ontop of everything else.
I've attached the code in "main", and in "sally":