JQuery :: Dropdown Menu Shows Up Without Using Mouse

This is the first time I work with jQuery [URL]. I have a little problem with my dropdown menu. As you see the orange dropdown menu shows up without using the mouse. I just want to make the dropdown pop out when you hover over the button.

This is the code.
The jQuery:
$(document).ready(function () {
$('#nav li').hover(
function () {
//show its submenu
$('ul', this).slideDown(200);
},
function () {
//hide its submenu
$('ul', this).slideUp(200);
});});