How to create a Windows Service in C# with Oracle DB Access?

I tried to create a Windows Service with Oracle Db Access, but when I run the service it's not running the DB access, only printing the services started message on assigned text file.

But I assigned this same code to C# console application, everything works fine even the DB access part, what am I missing?

This is my code:

public partial class Service1 : ServiceBase
{
    public Service1()
    {
        InitializeComponent();
    }

    protected override void OnStart(string[] args)
    {
        WriteToFile("Service is Started at" + DateTime.Now);

        string finalName = string.Empty;
        DataSet ds;
        try
        {
            DataAccess dataAccess = new DataAccess();
            OracleParameter[] paramArray = new OracleParameter[1];
            paramArray[0] = new OracleParameter("P_ResultSet", OracleDbType.RefCursor);
            paramArray[0].Direction = ParameterDirection.Output;

            ds = dataAccess.ReadDataBySP(paramArray, "SP_GET_ALL_SCREEN");

            if (ds != null)
            {
                foreach (DataRow row in ds.Tables[0].Rows)
                {
                    finalName += row["DISPLAYNAME"].ToString();
                }
            }
        }
        catch (Exception ex)
        {
            throw ex;
        }
        WriteToFile(finalName);
    }
    protected override void OnStop()
    {
        WriteToFile("Service is Stopped at" +DateTime.Now);
    }

    public static void WriteToFile(string Message)
    {
        string path = AppDomain.CurrentDomain.BaseDirectory + "\\Logs";
        if (!Directory.Exists(path))
        {
            Directory.CreateDirectory(path);
        }
        string filepath = AppDomain.CurrentDomain.BaseDirectory + "\\Logs\\ServiceLog_" + DateTime.Now.Date.ToShortDateString().Replace('/', '_') + ".txt";
        if (!File.Exists(filepath))
        {
            // creating file
            using (StreamWriter sw = File.CreateText(filepath))
            {
                sw.WriteLine(Message);
            }
        }
        else
        {
            using(StreamWriter sw = File.AppendText(filepath))
            {
                sw.WriteLine(Message);
            }
        }
    }
}

please Note that WriteToFile () method works fine.