Action Script 3 need some randomness

This is just a quick frame script assuming there's timeline clips named 'clip_1', 'clip_2' and 'clip_99', just for examples. It just has an array you can add as many clips to that you like (named anything) and it'll stop all other clips in the array while starting a different random clip that won't be the same clip. This is the easy way so it should be easy to follow (there's a million ways to do it).

Again assuming those clips and 'changeClipBtn' was the name of your button, just change to suit your needs. This is a script on frame 1 of the main timeline:

// keep track of the current clip
var lastClip:int = 0;
// filling an array with instance names on the timeline to choose between
// add as many as you like
var clips:Array = [ 'clip_1', 'clip_2', 'clip_99' ];// assuming on the main stage
// might want to iterate though clips turning their visible off, etc
// assign button handler, season name to taste
changeClipbtn.addEventListener( MouseEvent.CLICK, changeClipHandler ); 
function changeClipHandler(e:MouseEvent):void {
  // assure clips contains something to assure no infinite loops
  if ( clips.length == 0 ) { return; }// no clips, do nothing
  // we at least have one clip, stop all clips
  for ( var i:int = 0; i < clips.length; i++ ) {
  root[ clips ].gotoAndStop(1);
  }
  // only a single clip? play it again
  if ( clips.length == 1 ) { 
  this[ clips[0] ].gotoAndPlay(1); 
  return;
  }
  // if we get here we at least have 2 clips
  // rand generate a number pointing to a spot in the array 
  var nextClip:int = Math.floor( Math.random() * clips.length );
  // if the generated number is the same as the last number, generate again
  while ( nextClip == lastClip ) {
  nextClip = Math.floor( Math.random() * clips.length );
  }
  // just showing you the values
  trace('nextClip:' + nextClip + ', lastClip:' + lastClip);
  // track the new loading clip
  lastClip = nextClip;
  // here you can just play the clip or return the value, I'm asking it to play
  root[ clips[nextClip] ].gotoAndPlay(1);
}