May be this will help you
<html xmlns="http://www.w3.org/1999/xhtml">
<head runat="server">
<style type="text/css">
.hidePanel
{
display:none;
}
.showpanel
{
display : block;
}
.panel
{
background : gray;
padding : 10px;
}
div ul ul
{
display: none;
}
div ul li:hover > ul
{
display: block;
}
div ul li ul:hover > ul
{
display: block;
}
</style>
<title></title>
</head>
<body>
<form id="form1" runat="server">
<div>
<asp:scriptmanager id="ScriptManager1" runat="server" xmlns:asp="#unknown"></asp:scriptmanager>
<asp:modalpopupextender id="Modalpopupextender1" cancelcontrolid="Button8" targetcontrolid="Button2" popupcontrolid="StaffSP" runat="server" xmlns:asp="#unknown"></asp:modalpopupextender>
<asp:modalpopupextender id="Modalpopupextender2" cancelcontrolid="Button10" targetcontrolid="Button3" popupcontrolid="StaffFP" runat="server" xmlns:asp="#unknown"></asp:modalpopupextender>
<asp:modalpopupextender id="Modalpopupextender3" cancelcontrolid="Button12" targetcontrolid="Button5" popupcontrolid="AdminSP" runat="server" xmlns:asp="#unknown"></asp:modalpopupextender>
<asp:modalpopupextender id="Modalpopupextender4" cancelcontrolid="Button14" targetcontrolid="Button6" popupcontrolid="AdminSP" runat="server" xmlns:asp="#unknown"></asp:modalpopupextender>
<asp:label id="Label1" runat="server" font-bold="True" font-names="Arial" font-size="XX-Large" text="Automated Examination System" xmlns:asp="#unknown"></asp:label><br /> <br /><br />
<asp:panel id="Main" runat="server" height="181px" width="275px" xmlns:asp="#unknown">
<ul>
<li style="margin-removed: 33px; width: 169px;"> <asp:linkbutton id="LinkAdmin" runat="server" onclick="LinkAdmin_Click">Coordinator</asp:linkbutton></li>
<li style="width: 172px; margin-removed: 33px"> <asp:linkbutton id="LinkStaff" runat="server" onclick="LinkStaff_Click">Staff</asp:linkbutton></li>
<li style="margin-removed: 33px"> <asp:linkbutton id="LinkStudent" runat="server">Student</asp:linkbutton>
<ul>
<li><asp:linkbutton id="LinkButton1" runat="server">Fresh Registration</asp:linkbutton></li>
<li><asp:linkbutton id="LinkButton2" runat="server">Re Registration</asp:linkbutton></li>
</ul>
</li>
</ul>
</asp:panel>
</div>
<asp:panel id="StaffLogin" runat="server" height="59px" xmlns:asp="#unknown">
style="z-index: 1; left: 302px; top: 112px; position: absolute; height: 59px; width: 275px"
Visible="False" Width="275px">
Staff<br />
<asp:button id="Button1" runat="server" text="Login" />
<asp:button id="Button2" runat="server" text="New Staff" />
<asp:button id="Button3" runat="server" text="Fogot Password" />
</asp:panel>
<asp:panel id="AdminLogin" runat="server" xmlns:asp="#unknown">
style="z-index: 1; left: 302px; top: 193px; position: absolute; height: 78px; width: 275px"
Visible="False" Width="275px">
Admin<br />
<asp:button id="Button4" runat="server" text="Login" />
<asp:button id="Button5" runat="server" text="New Admin" />
<asp:button id="Button6" runat="server" text="Forgot Password" />
</asp:panel>
<asp:panel id="StaffSP" runat="server" height="48px" width="274px" CssClass="hidePanel" xmlns:asp="#unknown"><![CDATA[<%--/Here you missed visible false.--%>
Staff SP<br />
<asp:button id="Button7" runat="server" text="Button" />
<asp:button id="Button8" runat="server" text="Cancel" />
</asp:panel>
<asp:panel id="StaffFP" runat="server" height="48px" width="274px" CssClass="hidePanel" xmlns:asp="#unknown"><![CDATA[<%--Here you missed visible false.--%>
Staff FP<br />
<asp:button id="Button9" runat="server" text="Button" />
<asp:button id="Button10" runat="server" text="Cancel" />
<br />
<br />
</asp:panel>
<asp:panel id="AdminSP" runat="server" height="48px" width="274px" CssClass="hidePanel" xmlns:asp="#unknown"> <%----%>
Admin SP<br />
<asp:button id="Button11" runat="server" text="Button" />
<asp:button id="Button12" runat="server" text="Cancel" />
<br />
<br />
</asp:panel>
<asp:panel id="AdminFP" runat="server" height="48px" width="274px" CssClass="hidePanel" xmlns:asp="#unknown"> <%----%>
AdminFP<br />
<asp:button id="Button13" runat="server" text="Button" />
<asp:button id="Button14" runat="server" text="Cancel" />
</asp:panel>
</head></html>