Help with Show hide menu

Help with Show hide menu

I have a menu system using JQuery to hide and then slide out to show items. the problem i am having is that on some ie 9 machines in the office the buttons that should show when menu is clicked all show until page is totally loaded.
 
This is the code i have
 
$(document).ready(function(){
 
// Hide all unordered lists that are descended from the navigation
 $("#nav ul").hide();
 $("#artistnav ul").hide();
 
jQuery('a').bind('click', function(){
 
// on clicking the link get the parent li then find the first ul you can and display
 
$(this).parents("li:first").find("ul:first").slideToggle(1000);
 
//return false;
 
});
 
});
 
I would also like to find a way of closing a menu if another button os clicked to open another menu.
 
page can be seen here
 
 
thanks
 
colin