I can not show form when I call it by Method Invoker?

public void ShowForm2()
{
    // Declare my form
    Form2 a = new Form2();
    // Show form
    a.Show();
}

private void mnuSystem_Click(object sender, EventArgs e)
{
    _StatusProgressBar.ProgressBar.Show();

    // Method invoker
    MethodInvoker ink = new MethodInvoker(ShowForm2);
    IAsyncResult a = ink.BeginInvoke(null, null);

    _StatusProgressBar.ProgressBar.Value = 1;
    while (!a.IsCompleted)
    {
        if (_StatusProgressBar.ProgressBar.Value == 100)
        {
            _StatusProgressBar.ProgressBar.Value = 1;
        }
        else
        {
            _StatusProgressBar.ProgressBar.Value += 1;
            System.Threading.Thread.Sleep(10);
        }
    }
    ink.EndInvoke(a);
    _StatusProgressBar.ProgressBar.Hide();
}