I made a jquery popup box, and I am having trouble getting the background of the page to darken when the windw pops up.
The url to the page is http://rejuvenateusa.org/endorsements.html.
Heres the code I am using:
html:

<div class="cover"></div>
<div class="popup">
    <div class="close"><img src="images/test_eherenfeldbig.jpg" /><button>close</button></div>
</div>

    <div class="letters">
      <div class="open">
       <div class="letter"><a href="#" onmouseout="MM_swapImgRestore()" onmouseover="MM_swapImage('Image9','','images/test_ehrenfeldmag.jpg',1)"><img src="images/test_ehrenfeld.jpg" name="Image9" width="150" height="180" border="0" id="Image9" /></a></div>

       <div class="name">Rabbi Simcha Bunim Ehrenfeld</div>
        </div>

css:

.popup 
{
    position:fixed;
    border:solid 1px black;
    /*width:200px;
    height:200px;*/
    left:100px;
    top:100px;
    margin:-100px 0 0 -100px;
    display:none;
    background-color:red;
    z-index:2000;
}

.cover 
{
    background-color:black;
    width:100%;
    height:100%;
    display:none;
    position:fixed;
    z-index:5000;

}

jquery:

<script>
    $(document).ready(function () {

       $(".open").click(function () {
        $(".popup").fadeIn(500);
        $(".cover").fadeTo(500, 0.5);
    });

    $(".close").click(function () {
        $(".popup").fadeOut(500);
        $(".cover").fadeOut(500);
    });
});
    </script>

Any suggestions as to why the "cover" doesnt have the effect?
Thanks.

use another div outside popup div to completly cover the background and set its background dark.

At first gland I see that you haven't applied top and left CSS properties to the cover div. should be top and left set to 0.

Thanks for your responses, but none helped-
aslam, I do have another div, called "cover" that is supposed to be the blackened background. It's set to width and height of 100%, and set to display:none; so that it should only display when the window pops up. I cant wrap it around the entire popup, otherwise the whole pop-up will have display:none;
jorgem, i tried setting the cover to top and left set to 0, and it made no difference.
anything else????

IIRC, z-index only affects the layering of z-indexable elements (position:absolute, position:relative, or position:fixed). Layering of such elements with respect to those in the normal flow (position:static) can only be achieved by the ordering of nodes within the DOM.

Try moving your cover and popup divs to the very end of the HTML, immediately before </body>

Here is a sample using your code with a few adjustments...

Demo --> jsFiddle

<!doctype html>
<html>
<head>
<style>

.popup {
position:fixed;
border:solid 1px black;
width:200px;
height:200px;
left:45%;
top:25%;
display:none;
background-color:red;
}

.cover {
background-color:black;
width:100%;
height:100%;
display:none;
position:fixed;
top:0;
left:0;
}

.close {
color:#fff;
font-weight:bold;
background-color:#454545;
width:12px;
height:12px;
position:absolute;
top:-12px;
left:-12px;
padding:4px 6px 8px 6px;
border-radius:25px;
cursor:pointer;
}

</style>
<script src="http://ajax.googleapis.com/ajax/libs/jquery/1.7.2/jquery.min.js"></script>
</head>
<body>
<div class="cover"></div>
<div class="popup">
    <div class="close">
       <span>X</span>
    </div>
</div>

<div class="letters">
  <div class="open">
    <div class="letter">
       <a href="#" onmouseout="MM_swapImgRestore()" onmouseover="MM_swapImage('Image9','','images/test_ehrenfeldmag.jpg',1)">
          <img src="images/test_ehrenfeld.jpg" name="Image9" width="150" height="180" border="0" id="Image9" />
       </a>
    </div>
  </div>
  <div class="name">Rabbi Simcha Bunim Ehrenfeld</div>
</div>

<script>
    $(document).ready(function () {
       $(".open").click(function () {
        $(".popup").fadeIn(500);
        $(".cover").fadeTo(500, 0.5);
    });
    $(".close").click(function () {
        $(".popup").fadeOut(500);
        $(".cover").fadeOut(500);
    });
});
</script>

</body>
</html>

thanks for your help. the code works now.