buttons do not work! function script problem

help please!

I tried a new script. But it doesn't want to work. it is like this

photo.onPress = function(){
startPreload("slider.swf");
}

bio.onPress = function(){
startPreload("bio.swf");
};

design.onPress = function(){
startPreload("design.swf");
};

function startPreload(url){
Cont.loadMovie(url);
attachMovie("preloader anim", "prldr", 500, {_x:400, _y:300});

onEnterFrame = preloadContainer;
}

//and in same frame different layer

function preloadContainer(){
ar ldd = Cont.getBytesLoaded();

var ttl = Cont.getBytesTotal();

Cont.stop();
Cont._visible = false;

if (bytes_total > 0){
var prcnt = ldd/ttl;
preloader_mc.value = prcnt;

if (prcnt == 1){

Cont.play();

Cont._visible = true;

preloader_mc.removeMovieClip();
delete onEnterFrame;

}
}
}

that's it.

I checked. The movie clip that swfs are loaded into has instance "Cont"

other instances are also ok. photo, bio and design are instances of buttons.

Bio loads the swf but the preloader is not showing up. Photo doesn't load the swf and preloader at all ;/

help help help!