jQuery fadeOut works, fadeIn no error, no change, similarly fadeToggle doesn't come back on

This is driving me batty... this works fine:

<div id="box"> 
    <img src="/images/wpgen_box1.jpg">
</div>
<script type="text/javascript">
    jQuery(document).ready(function(){
        setTimeout(function(){ jQuery('#box').fadeOut(); }, 5000);
    });
</script>

But this does NOT work:

<div style="display:none" id="box">
    <img src="/images/wpgen_box1.jpg">
</div>
<script type="text/javascript">
    jQuery(document).ready(function(){
        setTimeout(function(){ jQuery('#box').fadeIn(); }, 5000);
    });
</script>

So, anyone know why I can fade out but not in?