Login Code Not Working

ExecuteScalar() did not work however I did try this and I got an exception:

try
                {
                    comm.CommandText = "SELECT count(*) FROM Accounts WHERE username = '" + txtUsername.Text + "', " + pboxPasscode.Password + "';";
                    int count = comm.ExecuteNonQuery();

                    if (count > 0)
                    {
                        this.Frame.Navigate(typeof(HomeStudent));
                    }
                }

                catch
                {

                }