Deseo hacer un login

using System;
using System.Collections.Generic;
using System.ComponentModel;
using System.Data;
using System.Drawing;
using System.Text;
using System.Windows.Forms;
using System.Runtime.InteropServices;
using System.Data.SqlClient;


namespace Analizador
{
public partial class Login : Form
{
SqlConnection conn;
SqlCommand command;
string query;

public Login()
{
InitializeComponent();
conn = Analizador.Program.conexion.getConnection();
command = conn.CreateCommand();
}

private void entrar_Click(object sender, EventArgs e)
{

string usuario = txtusuario.Text.ToString().Trim();
string contrasena = txtcontra.Text.ToString().Trim();


query = "SELECT COUNT(usu_id) FROM tabla_usuarios WHERE
usu_usuario= '"+ usuario +"' AND usu_password = '" + contrasena + "'";
command = new SqlCommand(query, conn);

string FilasContadas = command.ExecuteScalar().ToString();


if (FilasContadas.Equals("0"))
{
txtusuario.Clear();
txtcontra.Clear();
txtusuario.Focus();
MessageBox.Show("Los datos del usuario son inválidos");
return;
}
else
{
query = "SELECT usu_id, usu_usuario, usu_password,
usu_rol_id FROM tabla_usuarios WHERE usu_usuario= '" + usuario + "' AND
usu_password = '" + contrasena + "'";
command = new SqlCommand(query, conn);
SqlDataReader reader = command.ExecuteReader();

Form2 N = new Form2();
N.Show();
this.Hide();
}

}



private void cancelar_Click(object sender, EventArgs e)
{
Application.Exit();
}

private void Login_FormClosing(object sender, FormClosingEventArgs e)
{
//MessageBox.Show(this.DialogResult.ToString());
if (this.DialogResult==DialogResult.Cancel)
e.Cancel = true;

//if (this.DialogResult == DialogResult.None)
// Application.Exit();

}

}
}