What can be done for the password in my password?

        private void btn_Giris_Click(object sender, EventArgs e)
        {
            try
            {
                USER usr = DB.USERs.First(s => s.USERNAME == txtUserName.Text && s.PASSWORD == txtPassword.Text);
                if (usr.ISACTIVE == true)
                {
                    usr.ISONLINE = true;
                    DB.SubmitChanges();
                    Classes.ClsUser.UserName = usr.USERNAME;
                    Classes.ClsUser.UserID = usr.USERID;
                    this.Close();
                }
                else
                {
                    MessageBox.Show("Aktif Degilsin", "ADMIN", MessageBoxButtons.OK, MessageBoxIcon.Error);
                }
            }
            catch (Exception)
            {

                MessageBox.Show("kullanici adi veya parola hatasi");
            }
        }

What I have tried:

private void Parola_Animsa()
        {
            if (!Directory.Exists(Application.StartupPath + "\\Pasword")) 
            {
                Directory.CreateDirectory(Application.StartupPath + "\\Pasword");
            }

            string possibleFileName = (Application.StartupPath + "\\Pasword\\" + Classes.ClsUser.UserName + "#Public" + ".EdL");
            if (File.Exists(possibleFileName))
            {
                string content = File.ReadAllText(possibleFileName);
                txtPassword.Text = content;
            }
        }

        private void checkBox1_CheckedChanged(object sender, EventArgs e)
        {
            Parola_Animsa();
        }