-Have multiview control in your page with two views.Change the view according to selected value of the Radiobutton.
-When you select NEW COMPLAINT,then your second view will be displayed as below.
<asp:multiview id="MultiView1" runat="server" xmlns:asp="#unknown">
<asp:view id="View1" runat="server">
</asp:view>
<asp:view id="View2" runat="server">
<table>
<tr>
<td>
Name
</td>
<td>textbox</td>
</tr>
<tr>
<td>
Roll No.
</td>
<td>textbox</td>
</tr>
<tr>
<td>
Subject
</td>
<td>textbox</td>
</tr>
<tr>
<td>
Message
</td>
<td>textbox</td>
</tr>
<tr>
<td>button</td>
</tr>
</table></asp:view>
</asp:multiview>
on click event of the button.
string code1 = Guid.NewGuid().ToString();
using (MailMessage message = new MailMessage())
{
message.IsBodyHtml = true;
message.From = new MailAddress(from which you want to send mail);
message.To.Add(new MailAddress(to which you want to send mail));
message.Subject = subject here;
message.Body =body text here;
SmtpClient smtp = new SmtpClient();
smtp.Host = "host";
smtp.Credentials = new System.Net.NetworkCredential(username, password);
smtp.EnableSsl = false;
smtp.Send(message);
Response.Write("<script type='text/javascript'>");
Response.Write("alert('Thanks for feedback.');");
Response.Write("</script>");
}