Calculator help, buttons not working?

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

namespace Calculator2
{


    public partial class Form1 : Form
    {
        List<int> scores = new List<int>();
        private int Total = 0;
        private int Average = 0;
        public Form1()
        {
            InitializeComponent();
            TextBox[] tbs = new TextBox[] { txtTotal, txtCount, txtAverage };
            foreach (TextBox tb in tbs)
                tb.Enabled = false;
            txtScore.KeyPress += new KeyPressEventHandler(textBox1_KeyPress);
            txtScore.Focus();
        }
        private void textBox1_KeyPress(object sender, KeyPressEventArgs e)
        {
            if (e.KeyChar != (Char)Keys.Back && !Char.IsNumber(e.KeyChar))
                e.Handled = true;
            if (e.KeyChar == (Char)Keys.Enter)
                AddingNumbers();
        }
        private void btnAdd_Click(object sender, EventArgs e)
        {
            AddingNumbers();
        }

        private void AddingNumbers()
        {
            int ScoreInput;
            if (string.IsNullOrEmpty(txtScore.Text) || !int.TryParse(txtScore.Text, out ScoreInput))
            {
                txtScore.Focus();
                MessageBox.Show("Please enter a valid score", "Input Error");
                txtScore.Focus();
                return;
            }
            else if ((ScoreInput < 0) || (ScoreInput > 100))
            {
                txtScore.Focus();
                MessageBox.Show("The score must be between 0 and 100", "Input Error");
                txtScore.Focus();
                return;
            }
            scores.Add(20);
            int sum = 0;
            for (int i = 0; i < scores.Count; i++)
            {
                int score = scores[i];
                sum += score;
            }
            Total = ScoreInput + Total;
            Average = Total / scores.Count;
            txtTotal.Text = Total.ToString();
            txtAverage.Text = Average.ToString(string.Empty);
            txtCount.Text = scores.Count.ToString(string.Empty);
            txtScore.Text = string.Empty;
            txtScore.Focus();
        }
        private void btnDisplay_Click(object sender, EventArgs e)
        {
            scores.Sort();
            StringBuilder sb = new StringBuilder();
            for (int i1 = 0; i1 < scores.Count; i1++)
                sb.AppendLine(i1.ToString());
            MessageBox.Show(sb.ToString().Trim(), "Sorted Scores");
        }
        private void btnClear_Click(object sender, EventArgs e)
        {
            scores = null;
            TextBox[] tbs = new TextBox[] {txtScore, txtTotal, txtCount, txtAverage};
            foreach (TextBox tb in tbs)
                tb.Text = String.Empty;
            txtScore.Focus();
        }
        private void buttonExit_Click(object sender, EventArgs e)
        {
            this.Dispose();
        }
    }
}

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