Q : WMP not shuffling play selected item base on listbox

Question

Hi im working for simple media player, and i got a problem with my checkbox its not shuffling item...

here's my following code

listbox1

 private void listBox1_SelectedIndexChanged_1(object sender, EventArgs e)
    {

        blumemediaplayer.Ctlcontrols.play();
        MediaFile file = listBox1.SelectedItem as MediaFile;
        if (file != null)
        {
            wmp.URL = file.Path; 
            wmp.Ctlcontrols.play();  
        }

    }

checkbox for shuffling selected items but, its not working

bool IsShuffle = false;
        MediaFile file = listBox1.SelectedItem as MediaFile;
        if (checkBox2.Checked==true)
        {
            if (wmp.playState == WMPPlayState.wmppsPlaying)
            {
                // do nothing in this case since song is still playing
            }
            else
            {
                if (IsShuffle)
                {                       
                    Random rand = new Random();
                    listBox1.SelectedIndex = rand.Next(0, listBox1.Items.Count - 1);
                }
                else
                {

                    if (listBox1.SelectedIndex + 1 <= listBox1.Items.Count - 1)
                    {

                     listBox1.SelectedIndex = listBox1.SelectedIndex + 1;
                    }
                    else
                    {            
                        listBox1.SelectedIndex = 0;
                    }
                }
                wmp.URL = file.Path;
            }
        }

thank you :)