为什么我的函数beginLoading从不做可见的动作？

I am developing an ajax upload file using mootools, now I am trying to display a message in a html p tag that says loading, its just a simple message that fires whenever a user press button submit but never get visible when the submit button is fired, any advise?, I dont understand why, I also follow tutorial but I dont know, I just want in this simple way, please help

this is my code:

       #f1_upload_process{
           z-index:100;
           position:absolute;
           visibility:hidden;
           text-align:center;
           width:400px;
           margin:0px;
           padding:0px;
           background-color:#fff;
           border:1px solid #ccc;
       }
       </style>



   <p id="f1_upload_process">Loading...<br/></p>

   <p id="result"></p>

    <form method="post" action="" enctype="multipart/form-data">   

        <label for="file">Subir un archivo</label>
        <input type="file" name="file" id="fileArchivo" />
        <input type="submit" name="submit" id="btnSubir" value="upload file" />  

   <iframe name="iframUpload" id="iframeUpload" type="file" style="display:none"></iframe>


        </form>

and my mootols ajax

window.addEvent("domready",function(){
    cargarIndex();                                
});


function cargarIndex()
{   
   var prueboRequest = new Request({
   method: 'POST', 
   url: '../CONTROLLER/inicio.php',
   onRequest: function() {}, 
   onSuccess: function(texto, xmlrespuesta){
   document.getElementById('subirarchivo').innerHTML= texto;
   $('btnSubir').addEvent('click',function(){beginUploading()});  
   },
   onFailure: function(){alert('Error!');}  
   }).send();


}

function beginUploading(){


    document.getElementById('f1_upload_process').style.display = "visible";
        //$(''#f1_upload_process').css({display:'none'});
        return true;


//    return true;
} 

function beginUploading(){
$('#f1_upload_process').css('visibility','visible');
return true;
}

In css you have written visibility:hidden; not display:none; ...