Why is my laptop screen covered with a white “film” all of a sudden?

http://ift.tt/1iZHv9S

I have been using my laptop and in the middle of a session the screen became ‘covered’ with shady white color over the full screen so the laptop became unusable. I’ve tried rebooting and shutting down repeatedly but this has not helped.

It’s a Compaq Presario CQ42 laptop running Windows 7.