public frm_main()         // private constructor (singleton desPattern)
        {
            InitializeComponent();

            if (_instance == null)
            {
                _instance = this;
            }

            //file, prodcuts, users
            this.productsToolStripMenuItem.Enabled        = false;
            this.usersToolStripMenuItem.Enabled           = false;
            this.backUpDbToolStripMenuItem.Enabled        = false;
            this.restoreDbBackupToolStripMenuItem.Enabled = false;

            // used to update the textbox of current time and date
            Timer tmr;

            // timer to update the txt_dateTime textbox
            tmr          = new Timer();
            tmr.Interval = 1000;
            tmr.Tick    += tmr_Tick;
            tmr.Enabled  = true;
        }
 static void frm_FormClosed(object sender, FormClosedEventArgs e)
 {
     // for security purposes
     // dispose the form object on closing the form, just to make sure that no other forms are using this object
     _instance = null;
 }