C# ile Database Bağlantılı Form uygulamasında hata

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 System.Data.Sql;
using System.Data.SqlClient;

namespace WindowsFormsApp1
{
    public partial class Form1 : Form
    {

        SqlConnection adminbaglanti;
        SqlDataReader dr;
        SqlCommand com;

        public Form1()
        {
            InitializeComponent();
        }

        private void button1_Click(object sender, EventArgs e)
        {
            string username = textBox1.Text;
            string password = textBox2.Text;
            adminbaglanti = new SqlConnection("Data Source=E34004\\SQLEXPRESS;Initial Catalog=SalonTakipAdmin;Integrated Security=True");
            com = new SqlCommand();
            adminbaglanti.Open();
            com=new SqlCommand("Select*From Admin",adminbaglanti);

            dr = com.ExecuteReader();
            while (dr.Read())
            {
                if (username == dr["KullaniciAdi"].ToString() && password==dr["KullainiciSifre"].ToString())
                {
                    MessageBox.Show("Sayın admin hoşgeldiniz");
                }
                else
                {
                    MessageBox.Show("Kullanıcı Adı ve Şifreniz Yanlıştır  Kontrol Ediniz!");
                }
                adminbaglanti.Close();

            }
        }
    }
}

System.InvalidOperationException
  HResult=0x80131509
  İleti=Okuyucu kapalıyken Read öğesini çağırma girişimi geçersiz.
  Kaynak=System.Data
  StackTrace:
   at System.Data.SqlClient.SqlDataReader.TryReadInternal(Boolean setTimeout, Boolean& more)
   at System.Data.SqlClient.SqlDataReader.Read()
   at WindowsFormsApp1.Form1.button1_Click(Object sender, EventArgs e) in C:\Users\DELL\Desktop\Deneme\WindowsFormsApp1\WindowsFormsApp1\Form1.cs:line 38
   at System.Windows.Forms.Control.OnClick(EventArgs e)
   at System.Windows.Forms.Button.OnClick(EventArgs e)
   at System.Windows.Forms.Button.OnMouseUp(MouseEventArgs mevent)
   at System.Windows.Forms.Control.WmMouseUp(Message& m, MouseButtons button, Int32 clicks)
   at System.Windows.Forms.Control.WndProc(Message& m)
   at System.Windows.Forms.ButtonBase.WndProc(Message& m)
   at System.Windows.Forms.Button.WndProc(Message& m)
   at System.Windows.Forms.Control.ControlNativeWindow.OnMessage(Message& m)
   at System.Windows.Forms.Control.ControlNativeWindow.WndProc(Message& m)
   at System.Windows.Forms.NativeWindow.DebuggableCallback(IntPtr hWnd, Int32 msg, IntPtr wparam, IntPtr lparam)
   at System.Windows.Forms.UnsafeNativeMethods.DispatchMessageW(MSG& msg)
   at System.Windows.Forms.Application.ComponentManager.System.Windows.Forms.UnsafeNativeMethods.IMsoComponentManager.FPushMessageLoop(IntPtr dwComponentID, Int32 reason, Int32 pvLoopData)
   at System.Windows.Forms.Application.ThreadContext.RunMessageLoopInner(Int32 reason, ApplicationContext context)
   at System.Windows.Forms.Application.ThreadContext.RunMessageLoop(Int32 reason, ApplicationContext context)
   at System.Windows.Forms.Application.Run(Form mainForm)
   at WindowsFormsApp1.Program.Main() in C:\Users\DELL\Desktop\Deneme\WindowsFormsApp1\WindowsFormsApp1\Program.cs:line 19