My tabs are not working as they should - html

Question

I just finished writing my code for my navigation tabs using HTML5 and CSS3, but I'm having an issue! The tabs work perfectly in notepad, but when I put it in my website, it just doesn't work.
This is my CSS code:
nav ul ul {
display: none;
}
nav ul li:hover > ul {
display: block;
}
nav ul {
background: #efefef;
background: linear-gradient(top, #D8D8D8 10%, #D0D0D0 90%);
background: -moz-linear-gradient(top, #D8D8D8 10%, #D0D0D0 90%);
background: -webkit-linear-gradient(top, #D8D8D8 10%, #D0D0D0 90%);
box-shadow: 0px 0px 9px 0px rgba(0,0,0,0.15);
padding: 0px 20px;
border-radius: 10px;
list-style: none;
position: relative;
display: inline-table;
}
nav ul:after {
content: ""; clear: both; display: block;
}
li {
float: left;
}
nav ul li:hover {
background: #4b545f;
background: linear-gradient(top, #4f5964 0%, #5f6975 40%);
background: -moz-linear-gradient(top, #4f5964 0%, #5f6975 40%);
background: -webkit-linear-gradient(top, #4f5964 0%,#5f6975 40%);
}
nav ul li:hover a {
color: #fff;
}
nav ul li a {
display: block; padding: 10px 40px;
color: #757575; text-decoration: none;
font-family:arial;
}
nav ul ul {
background: #5f6975; border-radius: 0px; padding: 0px;
position: absolute; top: 100%;
}
nav ul ul li {
float: none;
border-top: 1px solid #6b727c;
border-bottom: 1px solid #575f6a;
position: relative;
}
nav ul ul li a {
padding: 10px 40px;
color: #fff;
font-family:arial; font-weight:900;
}
nav ul ul li a:hover {
background: #4b545f;
}
nav ul ul ul {
position: absolute; left: 100%; top:0;
}
The following is the HTML code I use to place them in the website:
<center><nav>
<ul>
<li>Home</li>
<li>Arcade
<ul>
<li>Action</li>
<li>Arcade</li>
<li>Puzzle</li>
<li>Vehicle</li>
<li>Violence</li>
<li>Defense</li>
<li>Point N Click</li>
<li>RPG</li>
</ul>
</li>
<li>Watch
<ul>
<li>TV Shows</li>
<li>Movies</li>
</ul>
</li>
<li>Extras
<ul>
<li>News</li>
<li>Updates</li>
</ul>
</li>
<li>Support</li>
</ul>
</nav></center>
If I delete the Home tab, the Arcade tab takes its place and looks the same way. Any ideas?
My website that this is happening on is: http://gameshank.com/8-20-13/
Thanks ahead!

Answer 1

On your site an additional link is inside your first li.
<a id="top"></a>
Also the center tag is deprecated. You should use:
margin: 0 auto;
For block level elements.