Prova cosi:
codice:
<script type="text/javascript" language="javascript"> 
var conta = 0
function disp(id){
      var box = document.getElementsByTagName("input")
for(var i=0; i<box.length; i++){
        if(box[i].type== 'checkbox' && box[i].checked){
conta++
}else{
conta--
}
}
if(conta>0){
          document.getElementById(id).style.display =  'block'; 
        }else{ 
          document.getElementById(id).style.display = 'none'; 
        } 
    } 
</script>