Send Email Windows Service

public MailSendQueueAgent()
{
    this.ServiceName = "Bulk Email Sending Agent V1.0";
    this.EventLog.Log = "Application";
    this.CanHandlePowerEvent = true;
    this.CanHandleSessionChangeEvent = true;
    this.CanPauseAndContinue = true;
    this.CanShutdown = true;
    this.CanStop = true;
}

protected override void OnStart(string[] args)
{
    base.OnStart(args);
    try
    {
        Thread T = new Thread(Execute);
        T.Start();
    }
    catch (Exception Ex)
    {
        EventLog.WriteEntry("Bulk Email Sending Agent V1.0",
            "Startup:Failed," + Ex.Message.ToString(),
            EventLogEntryType.Warning, 1003);
        writeLog(Ex.Message.ToString());
    }
}

private void Execute()
{
    DateTime sCurrentTime = Convert.ToDateTime("10:00:00 AM");
    DateTime eCurrentTime = Convert.ToDateTime(sCurrentTime.AddHours(10D));

    writeLog("Executing the Mail Sending service --- " + DateTime.Now);

    try
    {
        while (true)
        {
            DateTime systemStartTime = DateTime.Now;

            if (systemStartTime >= sCurrentTime && systemStartTime <= eCurrentTime)
            {
                ConnectionlHelper cnn = new ConnectionlHelper();
                cnn.OpenConn();

                try
                {
                    SqlCommand cd = new SqlCommand("sp_FetchSettings", cnn.oConnection);
                    cd.ExecuteNonQuery();

                    DataTable dts = new DataTable();
                    SqlDataAdapter dp = new SqlDataAdapter(cd);
                    dp.Fill(dts);

                    if (dts.Rows.Count > 0)
                    {
                        writeLog("Read Settings Successfull.....");

                        ConnectionlHelper conn = new ConnectionlHelper();
                        conn.OpenConn();

                        try
                        {
                            SqlCommand cmd = new SqlCommand("sp_SelectMailFromQueue", conn.oConnection);
                            cmd.ExecuteNonQuery();

                            DataTable dt = new DataTable();
                            SqlDataAdapter da = new SqlDataAdapter(cmd);
                            da.Fill(dt);

                            if (dt.Rows.Count > 0)
                            {
                                writeLog("New Mail to Sent at: " + DateTime.Now);

                                for (int i = 0; i < dt.Rows.Count; i++)
                                {
                                    try
                                    {
                                        MailMessage mail = new MailMessage();
                                        SmtpClient smtp = new SmtpClient(
                                            Convert.ToString(dts.Rows[0]["SmtpServer"]));

                                        smtp.DeliveryMethod = SmtpDeliveryMethod.Network;
                                        mail.From = new MailAddress(
                                            Convert.ToString(dts.Rows[0]["frm"]));

                                        mail.Bcc.Add(dt.Rows[i]["Email"].ToString());
                                        mail.Subject = dt.Rows[i]["MsgSubject"].ToString();
                                        mail.Body = dt.Rows[i]["MsgBody"].ToString();
                                        mail.IsBodyHtml = true;

                                        smtp.Port = Convert.ToInt32(dts.Rows[0]["Port"]);
                                        smtp.Credentials =
                                            new System.Net.NetworkCredential(
                                                Convert.ToString(dts.Rows[0]["DisplayName"]),
                                                Convert.ToString(dts.Rows[0]["Password"]));

                                        smtp.Send(mail);

                                        writeLog("Sending Mail count: " + i);

                                        UpdateMailStatus(Convert.ToInt32(dt.Rows[i]["MID"]));
                                        UpdateScheduleDetails(Convert.ToInt32(dt.Rows[i]["ScID"]));

                                        Thread.Sleep(5000);
                                    }
                                    catch (Exception Ex)
                                    {
                                        EventLog.WriteEntry(
                                            Ex.StackTrace.ToString(),
                                            EventLogEntryType.Error, 101);
                                        writeLog("Mail not sent " + Ex.Message);
                                    }
                                }
                            }

                            dt.Clear();
                        }
                        catch (Exception ex)
                        {
                            EventLog.WriteEntry(
                                "Error Connecting DB in con " + ex.Message.ToString());
                            writeLog("Error Connecting Database in con: " + ex.Message.ToString());
                        }
                        finally
                        {
                            conn.Close();
                        }
                    }

                    dts.Clear();
                }
                catch (Exception ex)
                {
                    EventLog.WriteEntry(
                        "Error Connecting DB in cnn " + ex.Message.ToString());
                    writeLog("Error Connecting Database in cnn: " + ex.Message.ToString());
                }
                finally
                {
                    cnn.Close();
                }
            }
        }
    }
    catch (Exception ex)
    {
        EventLog.WriteEntry(
            "Error Connecting DB Before While->" + ex.Message.ToString());
        writeLog("Error Connecting Database: " + ex.Message.ToString());
    }
}