Video does not open in DIV

I'm replacing my IFRAMES with DIVS, but I noticed that a scroll bar is not displayed when the page is extensive and the players of the videos on my page are not displayed inside the main DIV called content, why?

Follow my code:

Javascript

<script type="text/javascript">  
try{  
xmlhttp = new XMLHttpRequest();  
}  
catch(ee){  
try{  
xmlhttp = new ActiveXObject("Msxml2.XMLHTTP");  
}  
catch(e){  
try{  
xmlhttp = new ActiveXObject("Microsoft.XMLHTTP");  
}  
catch(E){  
xmlhttp = false;  
}  
}  
}  
div_base = "";  
function abre(arquivo,metodo,div){  
div_base = div;  
xmlhttp.open(metodo,arquivo);  
xmlhttp.onreadystatechange=conteudo  
xmlhttp.send(null)  
}  
function conteudo() {  
nova_div = div_base;  
document.getElementById(nova_div).innerHTML="<div style='top:50%;left:50%;
position:absolute; overflow:auto;'>carregando...</div>"  
if (xmlhttp.readyState==4){  
document.getElementById(nova_div).innerHTML=xmlhttp.responseText  
}  
}  
</script>

html

<a href="javascript: abre('minha_pagina.html','GET','conteudo');">
Minha   Pagina</a>

<div id="conteudo"></div>

Thank you