i have a problem with this code the right and left button not working.. at the last part of the code. could you please help me..

using System;
i have a problem with this code the right and left button not working..
at the last part of the code.
could you please help me..

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

namespace CustomerClient
{
    public partial class UsernameKeypad : Form
    {
        public UsernameKeypad()
        {
            InitializeComponent();
        }
        private void button1_Click(object sender, EventArgs e)
        {
            Close();
        }
        private void button8_Click(object sender, EventArgs e)
        {
        }
        private void textBoxUsername_TextChanged(object sender, EventArgs e)
        {
              textBox1.SelectionLength = 0;
              textBox1.SelectionStart = textBox1.Text.Length;
              textBox1.Focus();
              textBox1.ScrollToCaret();
         }

        private void button37_Click(object sender, EventArgs e)
        {
            Button cliked = (Button)sender;
            textBox1.Text += cliked.Text;
        }
        private void button29_Click(object sender, EventArgs e)
        {
        }
        private void button12_Click(object sender, EventArgs e)
        {
        }
        private void button13_Click(object sender, EventArgs e)
        {
        }
        private void button14_Click(object sender, EventArgs e)
        {
        }
        private void button15_Click(object sender, EventArgs e)
        {
        }
        private void button16_Click(object sender, EventArgs e)
        {
        }
        private void button17_Click(object sender, EventArgs e)
        {
        }
        private void button18_Click(object sender, EventArgs e)
        {
        }
        private void button19_Click(object sender, EventArgs e)
        {
        }
        private void button20_Click(object sender, EventArgs e)
        {
        }
        private void button21_Click(object sender, EventArgs e)
        {
        }
        private void button22_Click(object sender, EventArgs e)
        {
        }
        private void button23_Click(object sender, EventArgs e)
        {
        }
        private void button24_Click(object sender, EventArgs e)
        {
        }
        private void button25_Click(object sender, EventArgs e)
        {
        }
        private void button26_Click(object sender, EventArgs e)
        {
        }
        private void button27_Click(object sender, EventArgs e)
        {
        }
        private void button28_Click(object sender, EventArgs e)
        {
        }
        private void button30_Click(object sender, EventArgs e)
        {
        }
        private void button31_Click(object sender, EventArgs e)
        {
        }
        private void button32_Click(object sender, EventArgs e)
        {
        }
        private void button33_Click(object sender, EventArgs e)
        {
        }
        private void button34_Click(object sender, EventArgs e)
        {
        }
        private void button35_Click(object sender, EventArgs e)
        {
        }
        private void button36_Click(object sender, EventArgs e)
        {
        }
        private void button7_Click(object sender, EventArgs e)
        {
            if (textBox1.Text == "")
            {
                MessageBox.Show("Sorry!! Please Input your username.. :) ");
            }
        }
        private void button10_Click(object sender, EventArgs e)
        {
            button37.Text="q";
            button29.Text = "w";
            button12.Text = "e";
            button13.Text = "r";
            button14.Text = "t";
            button15.Text = "y";
            button16.Text = "u";
            button17.Text = "i";
            button18.Text = "o";
            button19.Text = "p";
            button20.Text = "a";
            button21.Text = "s";
            button22.Text = "d";
            button23.Text = "f";
            button24.Text = "g";
            button25.Text = "h";
            button26.Text = "j";
            button27.Text = "k";
            button28.Text = "l";
            button30.Text = "z";
            button31.Text = "x";
            button32.Text = "c";
            button33.Text = "v";
            button34.Text = "b";
            button35.Text = "n";
            button36.Text = "m";
            button2.Visible = true;
            button10.Visible=false;
        }
        private void button2_Click(object sender, EventArgs e)
        {
            button10.Visible = true;
            button2.Visible = false;
            button37.Text = "Q";
            button29.Text = "W";
            button12.Text = "E";
            button13.Text = "R";
            button14.Text = "T";
            button15.Text = "Y";
            button16.Text = "U";
            button17.Text = "I";
            button18.Text = "O";
            button19.Text = "P";
            button20.Text = "A";
            button21.Text = "S";
            button22.Text = "D";
            button23.Text = "F";
            button24.Text = "G";
            button25.Text = "H";
            button26.Text = "J";
            button27.Text = "K";
            button28.Text = "L";
            button30.Text = "Z";
            button31.Text = "X";
            button32.Text = "C";
            button33.Text = "V";
            button34.Text = "B";
            button35.Text = "N";
            button36.Text = "M";
        }
        private void button11_Click(object sender, EventArgs e)
        {
            textBox1.Text = textBox1.Text + " ";
        }
        private void button4_Click(object sender, EventArgs e)
        {
             int textlength = textBox1.Text.Length;
               if (textlength > 0)
                {
                    for (int i = 0; i < textlength;i++ )
                    {
                        textBox1.Text = textBox1.Text.Substring(0, textlength - 1);
                    }
                }
           textBox1.Focus();
        }

        private void leftbtn_Click(object sender, EventArgs e)
        {
            if (textBox1.SelectionStart > 0)
                textBox1.SelectionStart--;
        }
        private void rightbtn_Click(object sender, EventArgs e)
        {
        }
    }
}