7/Form1.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;

namespace BB_Azizova
{
    public partial class FAvtoriz : Form
    {
        public FAvtoriz()
        {
            InitializeComponent();
        }

        private void b1Vhod_Click(object sender, EventArgs e)
        {
            {
                if (string.IsNullOrEmpty(LogintextBox1.Text) || string.IsNullOrEmpty(PasswordtextBox2.Text))
                {
                    MessageBox.Show("Введите логин и пароль!");

                }

                using (var db = new BB_AzizovaEntities())
                {
                    var user = db.Administrator
                        .AsNoTracking()
                        .FirstOrDefault(u => u.Login == LogintextBox1.Text && u.Password == PasswordtextBox2.Text);
                    if (user == null)
                    {
                        MessageBox.Show("Пользователь с такими данными не найден!");
                        return;
                    }
                    F2Client f = new F2Client();
                    f.Show();
                    this.Hide();
                }
            }
        }
         
        private void b2Vahod_Click(object sender, EventArgs e)
        {
            this.Close();
        }
    }
}