Window Service started but not working on scheduled task

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Windows

Visual-Studio

VS2010

I created a Window Service project. When it is started, it will create/update an Oracle Table and the Oracle table can be viewed. However, the scheduled task does not work. The related code is below. In the FirstTask(), the trainArray retrieves on-line data from a website, and then update the Oracle table. Appreciate if you can hint me how to debug it.

protected override void OnStart(string[] args)  {
    System.Timers.Timer timScheduledTask = new System.Timers.Timer();
    timScheduledTask.Interval = 2 * 1000;
    timScheduledTask.Enabled = true;
    timScheduledTask.Elapsed += new System.Timers.ElapsedEventHandler(timScheduledTask_Elapsed);
}
void timScheduledTask_Elapsed(object sender, System.Timers.ElapsedEventArgs e)    {
    FirstTask(tblTrain, tblDestination, tblTrackCircuit_Geocode);
}

void FirstTask(DataTable tbl_Train, DataTable tbl_Dest, DataTable tbl_TrkGeo)  {
    string[,] trainArray = g.GetDataArrayFromWeb();
    long eTime = g.UnixTimestampFromDateTime(DateTime.Now);

    // Insert the array's data into Oracle table
    UpdateOracleTable(eTime, trainArray, tblTrackCircuit_Geocode, sTblName);
}