C#

in Form2:


public event EventHandler ButtonClicked;


//method that gets called when button on form2
//is clicked -> via: button.Click += new EventHandler
//(this.Button_Clicked); 
private void Button_Clicked(object sender, EvenArgs e)
{
   if(this.ButtonClicked != null)
        this.ButtonClicked(this, EventArgs.Empty);   
}

in Form1:

subscribe to ButtonClicked - Event of Form2 somewhere before you show Form2, just like this:

Form2 form2 = new Form2();
form2.ButtonClicked += new EventHandler(this.ChangeLabel);
form2.Show();

private void ChangeLabel(object sender, EventArgs e)
{
    this.label1.Text = "Button on Form2 has been clicked.";
}

SqlConnection conn = new SqlConnection(
  "Data Source=COMPUTERNAME; Initial Catalog=DBName; Integrated Security=SSPI");
SqlCommand cmd = conn.CreateCommand();
cmd.CommandText = "SELECT * FROM BankLogin WHERE usernm=@usernm AND pwd=@pwd";
SqlParameter usernm = cmd.Parameters.Add("@usernm", SqlDbType.NVarChar, 40);
SqlParameter pwd = cmd.Parameters.Add("@pwd", SqlDbType.NVarChar, 40);
SqlDataReader reader = null;
try
{
  usernm.Value = "username";
  pwd.Value = "password";
  reader = cmd.ExecuteReader();
}
catch (Exception ex)
{
  Console.Error.WriteLine("Error: {0}", ex.Message);
}
finally
{
  if (reader != null) reader.Close();
  conn.Close();
}