Sending mail through ASP.NET with C# not working

<%@ Page Language="C#" MasterPageFile="~/admin/AdminMasterPage.master" AutoEventWireup="true" CodeFile="~/admin/frmExamSchedule.aspx.cs" Inherits="admin_ExamSchedule" Title="Untitled Page" %>

<%@ Register Assembly="AjaxControlToolkit" Namespace="AjaxControlToolkit" TagPrefix="cc1" %>
<asp:Content ID="Content1" ContentPlaceHolderID="ContentBody" Runat="Server">
    <center>
<table border="2">
<tr><td style="font-size: x-large" colspan="3">Exam Schedule</td></tr>
<tr><td align="left">ExamId</td><td><asp:DropDownList ID="ddlExamIdNotAttempted" runat="server" Width="150" 
                                                                onselectedindexchanged="ddlExamIdNotAttempted_SelectedIndexChanged"></asp:DropDownList></td>
<%--    <td><asp:DropDownList ID="ddlExamIdAttempted" runat="server" Width="150" 
            ondatabound="ddlExamIdAttempted_DataBound"></asp:DropDownList></td>--%>
</tr>
<tr><td align="left">Date Of Assign</td>
<td><asp:TextBox ID="txtAssignExamDate" runat ="server" Width="150px" ></asp:TextBox>
&nbsp;&nbsp;
<cc1:CalendarExtender ID="CE1" runat="server" TargetControlID="txtAssignExamDate">
</cc1:CalendarExtender></tr>
<tr><td align="left">Key Code</td><td><asp:TextBox ID="txtKeyCode" runat="server" Width="150"></asp:TextBox></td></tr>
<tr><td colspan="2">
    <asp:Button ID="btnSubmit" runat="server" Text="Submit" 
        onclick="btnSubmit_Click" Height="31px" />&nbsp;</td></tr>
</table>
<asp:Label ID="LblMsg" runat="server" Text=""></asp:Label>
&nbsp;
        <asp:LinkButton ID="LBScheduleExam" runat="server" onclick="LB_Click">Go To 
        Schedule Exam</asp:LinkButton>
</center>
</asp:Content

using System;
using System.Collections;
using System.Configuration;
using System.Data;
using System.Linq;
using System.Web;
using System.Web.Security;
using System.Web.UI;
using System.Web.UI.HtmlControls;
using System.Web.UI.WebControls;
using System.Web.UI.WebControls.WebParts;
using System.Xml.Linq;
using System.Web.Mail;
using System.Web.Util;


public partial class admin_ExamSchedule : System.Web.UI.Page
{
    protected void Page_Load(object sender, EventArgs e)
    {
        if (!IsPostBack)
        {
                int examtypeid = Convert.ToInt32(Session["examtypeid"].ToString());
                ddlExamIdNotAttempted.DataSource = objAttemptexam.getNotAttemptedExamId(examtypeid);
                ddlExamIdNotAttempted.DataValueField = "ExamId";
                ddlExamIdNotAttempted.DataTextField = "ExamName";
                ddlExamIdNotAttempted.DataBind();
             
                //  Response.Write("<script>alert('Must Select Any One')</script>");
                //ddlExamIdAttempted.DataSource = objAttemptexam.getAttemptedExamId();
                //ddlExamIdAttempted.DataValueField = "ExamId";
                //ddlExamIdAttempted.DataTextField = "ExamName";
                //ddlExamIdAttempted.DataBind();
        }
    }
    BALexam objAttemptexam = new BALexam();
    protected void btnSubmit_Click(object sender, EventArgs e)
    {
            try
            {
                objAttemptexam.uid = Convert.ToInt32(Session["uid"].ToString());
                objAttemptexam.ExamReqDate = Convert.ToDateTime(Session["preferdate"]).ToString();
                objAttemptexam.ExamAssignDate =txtAssignExamDate.Text;
                objAttemptexam.ExamId = Convert.ToInt32(ddlExamIdNotAttempted.SelectedValue);
                objAttemptexam.ExamRequestId = Convert.ToInt32(Session["ExamRequestId"].ToString());
             //   objAttemptexam.UserName = Session["User"].ToString();
                objAttemptexam.KeyCode = txtKeyCode.Text;

                string strMsg;
                SendMails();
                int i = objAttemptexam.InsertScheduleExam(out strMsg);
                if (i > 1)
                {
                    ClearData();
                    LblMsg.Text = strMsg;
                }
                else
                    LblMsg.Text = strMsg;
            }
            catch (Exception ex)
            {
                LblMsg.Text = ex.Message;
            }
    }
    void SendMails()
    {
        MailMessage objMail = new MailMessage();
        objMail.From = "OnLineWebExamination.Com";
        objMail.To = "Localhost";
        objMail.Subject = "OnLineExam Schedule.";
        objMail.Body = "Your Key                 : " + txtKeyCode.Text + "" + "\n" +
                       "Your ExamId              : " + Convert.ToInt32(ddlExamIdNotAttempted.SelectedValue) + "" + "\n" +
                       "Your ExamDate            : " + txtAssignExamDate.Text;

        SmtpMail.SmtpServer = "LocalHost";
        SmtpMail.Send(objMail);
        Page.RegisterClientScriptBlock("Dhanush", "<script>alert('Key Send to Student Successfully...')</script>");
    }

    private void ClearData()
    {
        txtAssignExamDate.Text = txtKeyCode.Text = "";
    }
    protected void ddlExamIdAttempted_DataBound(object sender, EventArgs e)
    {
        ddlExamIdNotAttempted.Items.Insert(0, "--Select--");
    }
    protected void ddlExamIdNotAttempted_SelectedIndexChanged(object sender, EventArgs e)
    {

    }
    protected void LB_Click(object sender, EventArgs e)
    {
        Response.Redirect("frmShowExamRequest.aspx");
    }
}