//0 means disabled; 1 means enabled;   
var popupStatus = 0; 

//loading popup with jQuery 
function loadPopup(){   
    //loads popup only if it is disabled   
    if(popupStatus==0){   
        $("#popupWindow").fadeIn("slow");   
        popupStatus = 1;   
    }   
}

//disabling popup with jQuery
function disablePopup(){   
    //disables popup only if it is enabled   
    if(popupStatus==1){   
        $("#popupWindow").fadeOut("slow");   
        popupStatus = 0;   
    }   
}

//centering popup   
function centerPopup(){   
    //request data for centering   
    var windowWidth = document.documentElement.clientWidth;  
    var windowHeight = document.documentElement.clientHeight;   
    var popupHeight = $("#popupWindow").height();   
    var popupWidth = $("#popupWindow").width();  
    //centering   
    $("#popupWindow").css({   "position": "absolute",   "top": windowHeight/2-popupHeight/2,   "left": windowWidth/2-popupWidth/2   });   
} 

$(document).ready(function(){   
    //Click the x event!   
    $("#popupWindowClose").click(function(){   
        disablePopup();   
    });   
});

//Show popup window
function showPopup() {
    //centering with css   
    centerPopup();   
    //load popup   
    loadPopup(); 
}