I have the following markup using a twitter bootstrap modal plugin:
    
        
            <         
        
                      
      you probably forgot to include the javascript for the animations
<script src="assets/js/bootstrap-transition.js"></script>
<script src="assets/js/bootstrap-modal.js"></script>
the transitions.js needs to get included first!
First place your modal pop outside the body tag.After that comment or remove display property from class modal-backdrop in bootstrap.css as i have done below
.
modal-backdrop {
  position: fixed;
  top: 0;
  right: 0;
  bottom: 0;
  left: 0;
  z-index: 1040;
  background-color: #000;
  /*display:none;*/
now write some jquery as i have mentioned below:
$("#Yourid").click(function() {
  $('.modal-backdrop fade in').attr("display", "block");
});