(篇幅有点长，请大家耐心观看，在这里谢谢大家)大家帮我看看，我这代码哪里写错了？不会滚动，而且加载的gif图片还占用了各种的位置，导致banner显示不全。
<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd">
<html xmlns="http://www.w3.org/1999/xhtml">
<head>
<meta http-equiv="Content-Type" content="text/html; charset=utf-8" />
<title>无标题文档</title>
<link href="css/main.css" rel="stylesheet" type="text/css"/>
<script src="js/setHomeSetFav.js"type="text/javascript" charset="gb2312"></script>
<script src="js/mfocus-2.0.1.min.js"type="text/javascript"></script>
<script src="js/js/mf-pattern/mF_dleung.js"type="text/javascript"></script>
<script type="text/javascript">myFocus.ste({id:"picBox"})</script>
<link href="js/js/mf-pattern/mF_dleung.css"rel="stylesheet" type="text/css"/>
</head>
<body>
<div class="top">
<div class="top_content">
<ul>
<li><a href="#">联系我们</a></li>
<li><a href="#" noclick="AddFavorite(window.location,docunment.title)">加入收藏</a></li>
<li><a href="#" noclick="SetHome(window.location)">设为首页</a></li>
</ul>
</div>
</div><!--top结束-->
<div class="wrap">
<div class="logo">
<div class="logo_left">
<a href ="#"><img src="images/logo.jpg" alt="慕课网"/></a>
</div>
<div class="logo_right">
<img src="images/tel.jpg" alt="服务热线"/>24小时服务热线：<span class="tel">45-4444-56</span>
</div>
</div><!--logo结束-->
<div class="nav">
<div class=" nav_left"></div>
<div class="nav_mid">
<div class="nav_mid_left">
<ul>
<li><a href="#">首页</a></li>
<li><a href="#">关于慕课</a></li>
<li><a href="#">新闻动态</a></li>
<li><a href="#">课程中心</a></li>
<li><a href="#">在线课程</a></li>
<li><a href="#">人才招聘</a></li>
</ul>
</div>
<div class="nav_mid_right">
<form action="" method="post">
<input type="text" class="search_text"/>
</form>
</div>
</div><!--nav_mid结束-->
<div class="nav_right"></div>
</div><!--nav结束-->
<div class="ad" id="picBox">
<div class="loading"><img src="images/loading.gif" alt="图片加载中"></div>
<div class="pic">
<ul>
<li><img src="images/ad2.jpg"/></li>
<li><img src="images/ad3.jpg"/></li>
<li><img src="images/ad4.jpg"/></li>
</ul>
</div>
</div><!--ad结束-->
<div class="main">
<div class="news"></div>
<div class="course"></div>
<div class="sidebar"></div>
</div><!--main结束-->
</div><!--wrap结束-->
</body>
</html>
@charset "utf-8";
/* CSS Document */
*{
margin:0;
padding:0;
font-size:12px;
}
body
{
background-colr:#F5F5F5;
}
.top
{
width:100%;
height:27px;
background: url(../images/top_bg.jpg) repeat-x;
}
.top_content
{
width:1000px;
margin:0 auto;
}
.top_content li
{
list-style-image:url(../images/li_bg.gif);
float:right;
width:70px;
line-height:27px;
}
.top_content a:link,.top_content a:visited
{
color :#333;
text-decoration:none;
}
.top_content a:hover,.top_content a:active
{
color:#900;
text-decoration:none;
}
.wrap
{
width:1000px;
margin:0 auto;
}
.logo
{
height:80px;
background-color:#FFF;
}
.logo_left
{
width:200px;
float:left;
}
.logo_right
{
width:300px;
float:right;
heighl:28px;
margin-top:30px;
color:8e8e8e;
}
.logo_right img
{
vertical-align:middle;
margin-right:10px;
}
.tel
{
font-family:"微软雅黑";
font-size:16px; color:#c00;
}
.nav
{
height:40px;
}
.nav_left
{
width:10px;
background:url(../images/nav_left.jpg) no-repeat;
}
.nav_mid
{
width:980px;
background:url(../images/nav_bg.jpg) repeat-x;
}
.nav_right
{
width:10px;
background:url(../images/nav_right.jpg) no-repeat;
}
.nav_left,.nav_mid,.nav_right
{
float:left;
height:40px;
}
.nav_mid_left
{
width:680px;
}
.nav_mid_right
{
width:300px;
}
.nav_mid_right,.nav_mid_left
{
float:left;
}
.nav_mid_left li
{
float:left;
list-style-type:none;/*li消除小圆点*/
width:100px;
text-align:center;
line-height:40px;
}
.nav_mid_left a:link,.nav_mid_left a:visited/*链接的初始状态link，访问状态visited*/
{
text-decoration:none;/*清除下划线*/
color:#fff;
font-family:"微软雅黑";
font-size:16px;
}
.nav_mid_left a:hover,.nav_mid_left a:active/*鼠标经过状态hover，鼠标点击状态active*/
{
text-decoration:none;/*清除下划线*/
color:#FF0;
font-size:16px;
font-family:"微软雅黑";
}
.search_text
{
width:190px;
height:25px;
margin-top:7px;/*离顶部距离7px*/
background:url(../images/search.jpg) no-repeat right center;/*放大镜图标，不连续，右，中对齐*/
background-color:#fff;/*填充搜索框白色*/
padding-right:25px;/*//填充放大镜图标，以防输入盖过文字*/
border:1px;/*<!--边框线-->*/
}
.ad
{
height:310px;
overflow:hidden;/*<!--当内容溢出biv时，隐藏 --> */
}
