void Button1Click(object sender, System.EventArgs e)
 {
     if (this.textBox1.Text == "" && this.password.Text == "")
     {
         Examen x = new Examen();
         x.Show();
         this.Hide();
     }
     else
     {
         System.Windows.Forms.MessageBox.Show("usuario incorecto");
     }
 }