why DocumentNode.SelectNodes returns null ?

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C#

WinForms

I use htmlagilitypack
I want to get all atributes href of tag [a] in content html
So, I use method SelectNodes() but it return null

This is source content html:

<table class="table">
	<tr>
		<td class="frame">
			<table class="frame" id="highlight">
				<tr class="colhead">
					<td id="categ_icon">
						<a href="#" class="colhead">Category</a>
					</td>
					<td id="name">
						<a href="?sort=name&h=2&d=ASC" class="colhead">Name</a>
					</td>
					<td id="links">
						<a href="#" class="colhead">Links</a>
					</td>
					<td id="files">
						<a href="?sort=numfiles&h=3&d=DESC" class="colhead">Files</a>
					</td>
					<td id="comments">
						<a href="?sort=comments&h=4&d=DESC" class="colhead">Comm.</a>
					</td>
					<td id="added">
						<a href="?sort=added&h=6&d=DESC" class="colhead">Added</a>
					</td>
					<td id="size">
						<a href="?sort=size&h=8&d=DESC" class="colhead">Size</a>
					</td>
					<td id="snatch">
						<a href="?sort=times_completed&h=9&d=DESC" class="colhead">Snatch</a>
					</td>
					<td id="seeders">
						<a href="?sort=seeders&h=10&d=DESC" class="colhead">Seed</a>
					</td>
					<td id="leechers">
						<a href="?sort=leechers&h=11&d=DESC" class="colhead">Leech</a>
					</td>
									</tr>
				<tr class="torrent_1"><td class="table_categ_icon"><a class="link" href="?cat=545" onmouseover="return overlib('Game of Thrones');"  önmouseout="return nd();"><img src="http://static.freshon.tv/pic/catids/545.gif" width="80" height="44" alt="category_icon" /></a></td><td class="table_name"><div>
											<a <big>href="/details.php?id=108260"</big> class="torrent_name_link"title="Game.of.Thrones.S03E08.PROPER.HDTV.x264-2HD">Game.of.Thrones.S03E08.PROPER.HDTV.x264-2HD</a>
										</div>

										<div class="table_genre_nf"><a href="/browse.php?filter=drama" class="normal">Drama</a> | <a href="/browse.php?filter=family" class="normal">Family</a> | <a href="/browse.php?filter=fantasy" class="normal">Fantasy</a></div></td><td class="table_links"><a href="/download.php?id=108260&type=torrent" class="link">
									<img src="http://static.freshon.tv/pic/download_12.png" alt="DW" onmouseover="return overlib('Download torrent');"  önmouseout="return nd();" width="12" height="12"/>
								</a><a href="/bookmarks.php?type=add&tid=108260" class="link">
									<img src="http://static.freshon.tv/pic/bookmark_add_12.png" alt="BK_add" onmouseover="return overlib('Bookmark torrent');"  önmouseout="return nd();" width="12" height="12"/>
									</a></td><td class="table_files">
									<a href="/details.php?id=108260&files=1#files_tab" class="link">
										2
									</a>
							</td><td class="table_comments">
									<a href="details.php?id=108260&page=0#comments_tab" class="link">
										0
									</a>

I want to get : href="/details.php?id=108260"(I did big size font in above html)

This is my code:

public string GetLinkOfNews(string xpath)
{
    string content = GoToBrowseWebsite("http://abc.com");

    string htmldoc = "";

    HtmlAgilityPack.HtmlDocument document = new HtmlAgilityPack.HtmlDocument();
    document.LoadHtml(content);

    HtmlNodeCollection nodeCollection = document.DocumentNode.SelectNodes(xpath);
    foreach (HtmlNode node in nodeCollection)
    {
       htmldoc += node.ToString();
    }

    return htmldoc;
}

public string GoToBrowseWebsite(string url)
{
    HttpWebRequest requestBR = (HttpWebRequest)WebRequest.Create(url);
    requestBR.Method = "GET";
    requestBR.ContentType = "application/x-www-form-urlencoded";
    requestBR.CookieContainer = ReadCookiesFromDisk("E:\\cookie.txt");
    HttpWebResponse responseBR = (HttpWebResponse)requestBR.GetResponse();

    StreamReader reader = new StreamReader(responseBR.GetResponseStream());
    string htmldoc = reader.ReadToEnd();
    responseBR.Close();
    return htmldoc;
}

this is my xpath :

/table/tr/td/div/a[@href]

somebody help me!!!