private void txtBox_KeyPress(object sender, KeyPressEventArgs e)
 {
    e.Handled = (e.KeyChar == '0');
 }

private void txtBox_TextChanged(object sender, KeyPressEventArgs e)
 {
    if (String.IsNullOrEmpty(textbox.Text) || txtmoney.Text == "0")
    {
        // Do Something
    }
 }

txtBox.KeyPress += txtBox_KeyPress;
txtBox.TextChanged += txtBox_TextChanged;