Only My Wallpaper Is Displayed On

I've owned a HP 540 laptop and when I switch it on it doesn't show any display. I've tried to connect a display monitor to the VGA port of the laptop to check its display if it is okay.
I've done on pressing the f5 together with fn button to switch to external monitor for display. Still there is nothing on my screen except for the wallpaper which I setup before.
