二级菜单被遮住的问题

有三个文件index.htm、left.htm和main.htm。问题是左侧的二级菜单被遮住了，如何让其显示上来？谢谢！文件内容如下：
/////////////////////////////////////////////////////////////////////
//index.htm
/////////////////////////////////////////////////////////////////////
<html>
<head>
<title>aa</title>
</head>
<frameset rows="91,*" cols="*"  frameborder="no" framespacing="0" >
  <frame src="top.htm" frameborder="0" marginheight="0" marginwidth="0" scrolling="no" noresize>
  <frameset rows="*" cols="117,669">
    <frame src="left.htm" frameborder="0" marginheight="0" marginwidth="0" scrolling="yes" noresize>
    <frame src="main.htm" noresize>
  </frameset>
</frameset>
<noframes><body>
</body></noframes>
</html>/////////////////////////////////////////////////////////////////////
//left.htm
/////////////////////////////////////////////////////////////////////
<meta http-equiv="Content-Type" content="text/html; charset=gb2312">
<HTML>
<HEAD>
<TITLE>aa</TITLE>
</HEAD>
<SCRIPT LANGUAGE="JavaScript"> document.onmousemove = test;
var x;
var y;
var toHideTrObj;
var previewMenuTrObj;
//var isSubMenuOpened=false;
var toShowTrObj; function test(){
x=window.event.x;
y=window.event.y;
}
function mouseOver(){

var obj = toShowTrObj;
previewMenuTrObj=obj;

obj.children[0].bgColor="#A3C6DB";
obj.children[0].style.backgroundColor="#E8F1F6";
showSubMenu(obj);
}
function mouseLeave(){
var obj=toHideTrObj;
obj.children[0].bgColor="#6600FF";
var div = obj.nextSibling.children[0].children[0];
var divLeft = div.offsetParent.offsetLeft+div.offsetLeft;
var divRight = div.offsetParent.offsetLeft+div.offsetLeft+div.offsetWidth;
var divTop = div.offsetParent.offsetTop+div.offsetTop;
var divBottom = div.offsetParent.offsetTop+div.offsetTop+div.offsetHeight;
if(obj.nextSibling.children[0].children[0].style.display=="block"&&
(
x >= divLeft
&& x <= divRight
&& y >= divTop
&& y <= divBottom
)
){

return;
}
hideSubMenu(obj);
} function showSubMenu(obj){ var div = obj.nextSibling.children[0].children[0];
var o = obj.children[0];
div.children[0].style.bgColor="#A3C6DB";
div.children[0].style.backgroundColor="#E8F1F6";
div.style.left=obj.offsetParent.offsetLeft+o.offsetLeft+o.offsetWidth;
div.style.top=obj.offsetParent.offsetTop+o.offsetTop;
div.style.display="block"; } function hideSubMenu(){
var obj = previewMenuTrObj;
if(null==obj){
return;
} var trLeft = obj.offsetParent.offsetLeft+obj.offsetLeft;
var trRight = obj.offsetParent.offsetLeft+obj.offsetLeft+obj.offsetWidth;
var trTop = obj.offsetParent.offsetTop+obj.offsetTop;
var trBottom = obj.offsetParent.offsetTop+obj.offsetTop+obj.offsetHeight;

if(
x > trLeft
&& x < trRight
&& y > trTop
&& y < trBottom
){
return;
}
obj.nextSibling.children[0].children[0].style.display="none"; } function doOpen(obj){
if(obj.forward==null||obj.forward==""){
return;
}
var screenwidth = screen.width;
var screenheight = screen.height;
var top = 0;
var left = 0;
var height = screenheight*0.93;
var width = screenwidth*0.99;
window.open (obj.forward, '', 'width='+width+',height='+height+',top='+top+', left='+left+', toolbar=no, menubar=no,scrollbars=yes, resizable=no,location=no, status=no').document.focus();
}
</SCRIPT>
<BODY style="border-right-style:solid;border-right-width:1px;border-right-color:#818181;">
<table border="0" cellpadding="0" cellspacing="0" align="center" width="20%">  <tr align="center" style="cursor:hand;"  onmouseleave="toHideTrObj=this;setTimeout(mouseLeave,500)" onmouseover="hideSubMenu();toShowTrObj=this;setTimeout(mouseOver,500);">
<td background="../images/middle01.gif" HEIGHT="30" BORDER=0 class="menu2_td" nowrap><B>一级菜单a</B></td> 
</tr>
<tr>
<td>
<div style="display:none;position:absolute;" onmouseLeave="this.style.display='none';">
<table cellpadding="0" cellspacing="0" border="0" align="center" width="100%">
<tr onclick="doOpen(this)" align="center" forward="../LXSL/LXSL011.htm">
<td style="cursor:hand" class="menu3_td" height="30" nowrap>二级菜单1</td>
</tr>
</table>
</div></td>
</tr>
<tr align="center" style="cursor:hand;"  onmouseleave="toHideTrObj=this;setTimeout(mouseLeave,500)" onmouseover="hideSubMenu();toShowTrObj=this;setTimeout(mouseOver,500);">
<td background="../images/middle01.gif" HEIGHT="30" BORDER=0 class="menu2_td"nowrap><B>一级菜单b</B></td>
</tr>
<tr>
<td>
<div style="display:none;position:absolute;" onmouseLeave="this.style.display='none';"> <table cellpadding="0" cellspacing="0" border="0" align="center" width="100%">
<tr onclick="doOpen(this)" align="center" forward="../SLMK/SLMK010.htm">
<td style="cursor:hand"   class="menu3_td" height="30" nowrap>二级菜单1</td>
</tr>
<tr onclick="doOpen(this)"  align="center" forward="../SLMK/SLMK020.htm">
<td style="cursor:hand"   class="menu3_td" height="30" nowrap>二级菜单2</td>
</tr>
</table>
</div>
</td>
</tr>
</table>
</BODY>
<SCRIPT LANGUAGE="JavaScript">
</SCRIPT>
</HTML>/////////////////////////////////////////////////////////////////////
//main.htm
/////////////////////////////////////////////////////////////////////
<HTML>
<HEAD>
<TITLE>aa</TITLE>
</HEAD>
<BODY>
<TABLE border="0" width="90%" align="center" cellPadding="0" cellSpacing="0">
<TR>
<TD class="title_td">啊啊啊啊</TD>
</TR>
</TABLE>
</BODY>
</HTML>
谢谢大家！