{
 OleDbConnection con = new OleDbConnection(@ "Provider=Microsoft.ACE.OLEDB.12.0;Data Source=.MSAccessTestDB.accdb");

 private void button1_Click(object sender, EventArgs e) {
  con.Open();

  OleDbDataAdapter sda = new OleDbDataAdapter("SELECT * FROM LOGIN where username='" + textBox1.Text + "' and password='" + textBox2.Text + "'", con);
  DataTable dt = new DataTable();
  sda.Fill(dt);
  if (dt.Rows.Count == 1) {
   this.Hide();
   Form2 ss = new Form2();
   ss.Show();
  } else {
   MessageBox.Show("Invalid username/Password");
  }

  con.Close();
 }
}