How fix this menu bar to show the dropdown sub-menu?

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Javascript

CSS

HTML

jQuery

I used one of the CSS templates and the menu in it has no dropdown menu so I added the dropdown mene to it. The problem now is sometimes when I put the mouse over one of the tabs/options that has a dropdown menu (sub-menu), I cannot select anything from this dropdown menu because it is quickly disappeared and I don't know why this happened.

The HTML code for this menu:

<div class="topnav">
                <ul class="menu"  runat="server" >
                    <li><a href="Default.aspx">Home</a></li>
                    <li><a href="Services.aspx">Services</a>
                        <ul>
                            <li><a href="#">Service #1</a></li>
                            <li><a href="#">Service #2</a></li>
                            <li><a href="#">Service #3</a></li>
                        </ul>
                    </li>
                    <li><a href="#">Items</a>
                        <ul>
                            <li><a href="#">Item #1</a></li>
                            <li><a href="#">Item #2</a></li>
                            <li><a href="#">Item #3</a></li>
                            <li><a href="#" target="_blank">Item #4</a></li>
                            <li><a href="#" target="_blank"">Item #5</a></li>
                            <li><a href="#" target="_blank">Item #6</a></li>
                            <li><a href="#">Item #1</a></li>
                        </ul>
                    </li>

                    <li><a href="#">About</a></li>
                    <li><a href="#">Contact Us</a></li>
                    <li><a href="#">Help</a></li>

                </ul>
                <div class="clr"></div>
              </div>

The css code for this menu is:

@charset "utf-8";
    /* CSS Document */
    
    
    ul.menu li ul { font-family:"Liberation sans", Arial, Helvetica, sans-serif;}
    
    
    /* DESIGN TOPNAV (mainmenu) */
    .topnav { padding:0; margin:0; width:966px; height:53px; background: url(images/bg_menu.gif) top repeat-x; }
    
    
    /* level 0 */
    .topnav ul { padding:0; margin:0 30px 0 0; list-style:none; border:0; float: left; }
    .topnav ul li { float:left; margin:0; padding:0; border-right:1px solid #303030; border-left:1px solid #0a0a0a; }
    .topnav ul li a { float:left; margin:0 1px 0 0; padding:17px 30px; color:#fff; font:normal 14px Georgia, "Times New Roman", Times, serif; text-decoration:none; }
    .topnav ul li.current_page_item { }					/* active item first level */
    .topnav ul li.current_page_item a,
    .topnav ul li a.a_hover_main { color:#fff; background-color:#0f0f0f;}						/* on hover */
    
    
    /* level 1 */
    .topnav ul li ul { padding:0; top:52px; left:-2px; height:auto; color:#a8a7a7; background-color:#0f0f0f; border-bottom:none;}			/* position of submenu */
    .topnav ul li ul li { margin:0; padding:0; background:none; border-bottom:1px solid #010101;}
    
    /* for the next line: (.topnav ul li ul li a)
     * I changed:  
     * padding: 10px 24px and width: 49px
     * and I added: margin:0 1px 0 0
     */
    .topnav ul li ul li a { float:left; margin:0 1px 0 0; padding:17px 47px; width:54px; font:normal 12px Georgia, "Times New Roman", Times, serif; color:#7f7f7f;}
    .topnav ul li ul li a.have_submenu { }																/* if item have submenu */
    .topnav ul li ul li a:hover,
    .topnav ul li ul li a.have_submenu_hover { color:#fff; background:none;}
    .topnav ul li ul li ul { padding:0; top:-1px; left:170px;}	/* position of submenu level 2 */
    
    .topnav * { z-index:1001;}
    
    /* DO NOT EDIT!!! */
    ul.menu { list-style:none;}
    ul.menu li { cursor:pointer; position:relative;}
    ul.menu li a { position:relative;}
    ul.menu li ul { display:none; position:absolute; list-style:none;}
    ul.menu li ul li ul { position:absolute; list-style:none;}

JQuery code:

jQuery(document).ready(function($){
    
        // menu smothness
        $('.menu li').click(function() {
          window.location = $(this).find('a:first').attr('href');
        });
        var dropdown_level = 0;
        $('.menu li ul').parent().find('a:first').addClass('have_submenu');
        $('.menu').children('li').children('a').addClass('top_level');
        $('.menu').children('li').children('a').removeClass('have_submenu');
        $('.menu li').hover(function(){
          if(dropdown_level == 0){
            $('.menu').find('a').removeClass('have_submenu_hover');
            $(this).addClass('li_hover_main');
            $(this).children('a').addClass('a_hover_main');
            $('.menu ul').parent().find('a:first').addClass('have_submenu');
            $('.menu').children('li').children('a').addClass('top_level');
            $('.menu').children('li').children('a').removeClass('have_submenu');
          }
          $(this).find('ul:first').stop(true,true).slideDown(200).show();
          $(this).find('a:first').addClass('have_submenu_hover');
          $('.menu').children('li').children('a').removeClass('have_submenu_hover');
          dropdown_level++;
        },function(){
          $(this).find('ul:first').stop(true,true).slideUp(0);
          $(this).find('a:first').removeClass('have_submenu_hover');
          dropdown_level--;
          if(dropdown_level == 0){
            $(this).removeClass('li_hover_main');
            $(this).children('a').removeClass('a_hover_main');
           }
        });
    	// END of menu smothness
      
    });