Event Not Fired On Editing Control Of Datagridview

Question

There is strange problem I am facing that I have custome datagridview in my application and I am trying to fire even on Editing ControlShowing Event Of datagridview as below:

        private void newdgv_EditingControlShowing(object sender, DataGridViewEditingControlShowingEventArgs e)

        {

            TextBox tbox = e.Control as TextBox;

            if (newdgv.CurrentCell.ColumnIndex == 0) 

            {

                    

                tbox.TextChanged+=new EventHandler(tbox_TextChanged);

                tbox.KeyDown += new KeyEventHandler(tbox_KeyDown);

                

            }

        }

        private void tbox_KeyDown(object sender, KeyEventArgs e)

        {

            if (e.Control && e.KeyCode == Keys.C)

            {

                CashShortAC4 csa4 = new CashShortAC4();

                csa4.Bt_Click += new CashShortAC4.CShortAC1(csa4_Bt_Click);

                csa4.Show(this);

            }

        }

        private void tbox_TextChanged(object sender, EventArgs e)

        {

            TextBox tbox = (TextBox)sender;

            if (tbox.Text.Length > 2)

            {

                listBox2.Visible = true;

                button2.Visible = true;

                int inddex = listBox2.FindString(tbox.Text);

                if (inddex != -1)

                {

                    listBox2.SetSelected(inddex, true);

                    listBox2.Focus();

                    tbox.TextChanged -= new EventHandler(tbox_TextChanged);

                }

            }

        }

The tbox TextChanged event working very well but tbox keydown event not working. When I Press Ctrl+C on Editing Control like textbox it's not showing me the concern new form CashShortAC4.  I don't know what is wrong in my application. How to solve the problem?.