Simple Login in Code Behind

frmLogin.cs

using System;
using System.Collections.Generic;
using System.ComponentModel;
using System.Data;
using System.Drawing;
using System.Linq;
using System.Text;
using System.Threading.Tasks;
using System.Windows.Forms;

using PoS.Entities;
using PoS.Services;

namespace PoS
{
    public partial class frmLogin : Form
    {
        public frmMain frmMain;

        public User User { get; set; }

        bool Logged { get; set; }

        UsersService _usersService;

        public frmLogin()
        {
            InitializeComponent();

            _usersService = new UsersService();
        }

        private void frmLogin_Load(object sender, EventArgs e)
        {
            LoadUsers();
        }

        private void btnLogin_Click(object sender, EventArgs e)
        {
            if (!string.IsNullOrEmpty(txtPassword.Text))
            {
                Logged = Login();

                if (Logged)
                {
                    MessageBox.Show("Login Success!", "", MessageBoxButtons.OK, MessageBoxIcon.Information);
                    this.DialogResult = DialogResult.OK;
                    this.Close();
                }
                else
                {
                    MessageBox.Show("Incorrect password, type your correct password.", "", MessageBoxButtons.OK, MessageBoxIcon.Warning);
                    txtPassword.Focus();
                    this.DialogResult = DialogResult.None;
                }
            }
            else
            {
                MessageBox.Show("Please type a password.", "", MessageBoxButtons.OK, MessageBoxIcon.Exclamation);
                txtPassword.Focus();
                this.DialogResult = DialogResult.None;
            }
        }

        private void btnCancel_Click(object sender, EventArgs e)
        {
            this.DialogResult = DialogResult.No;
        }

        private void frmLogin_FormClosing(object sender, FormClosingEventArgs e)
        {
            if (!Logged)
                this.DialogResult = DialogResult.No;
        }

        private void LoadUsers()
        {
            cmbUsers.DataSource = _usersService.GetAll();
            cmbUsers.DisplayMember = "Username";
            cmbUsers.ValueMember = "Id";
        }

        private bool Login()
        {
            this.User = _usersService.Find(Convert.ToInt32(cmbUsers.SelectedValue));

            return _usersService.Login(Convert.ToInt32(cmbUsers.SelectedValue), txtPassword.Text);
        }
    }
}

UsersService.cs

using System;
using System.IO;
using System.Reflection;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Threading.Tasks;

using Simple.Data;
using PoS.Entities;

namespace PoS.Services
{
    public class UsersService
    {
        dynamic db;

        public UsersService()
        {
            db = Database.OpenFile(GetDBPath());
        }

        private string GetDBPath()
        {
            return @"C:\MyPath\PosDB.sqlite";
        }

        public bool Login(int userId, string password)
        {
            User user = db.Users.FindById(userId);

            return user.ValidatePassword(password);
        }
    }
}