InvlidateRect() Doesn't Allow to Display My Child Screen in MFC?

Hi,

I'm Getting Real-time Data and Display the image in main screen. Using the InvalidateRect() method, I'm refresh the main screen(Image Area only - 768 * 256) continuously.

Now I opened a child screen . It was display the back side of main screen.

If i press ALT key means it appear in front.

With out Alt key press, how can I display the child screen?

Please Help me.