SqlConnection con = new SqlConnection("server=servername;initial catalog=databasename;user=username;password=yourpassword;");
con.Open();
SqlCommand cm = new SqlCommand("select username,password from tablename where username=@user and password =@pass",con);
SqlDataReader dr = cm.ExecuteReader();
if (dr.Hasrows)
{
MessageBox.Show("Login OK");
}
else
{
MessageBox.Show("Don't Login");
}
dr.Close();