private void FormPrincipal_Load(object sender, EventArgs e)
        {
            this.Hide();
            Login nueva = new Login(this);

            nueva.TopMost = true;
            nueva.Show();

            PanelControl newMDIChild = new PanelControl();

            newMDIChild.MdiParent   = this;
            newMDIChild.WindowState = FormWindowState.Maximized;
            newMDIChild.Show();
        }
        private void panelToolStripMenuItem_Click(object sender, EventArgs e)
        {
            Form existe = Application.OpenForms.OfType <Form>().Where(pre => pre.Name == "PanelControl").SingleOrDefault <Form>();

            if (existe != null)
            {
                existe.WindowState = FormWindowState.Maximized;
                existe.BringToFront();
            }
            else
            {
                PanelControl newMDIChild = new PanelControl();
                newMDIChild.MdiParent   = this;
                newMDIChild.WindowState = FormWindowState.Maximized;
                newMDIChild.Show();
            }
        }