This is one of the strangest things I have ever seen.
I have an HP Elitebook 8460p and recently updated my Windows 8 to Windows 8.1.
Now when I have certain windows open and focused (it's always different, sometimes it's chrome, sometimes it's the control-panel and so on, there is no clear pattern) the backlight of the screen is completely turned off - when I take a torch and point it to the screen or hold it to a bright-light source I can see there is still a picture there you can even work (or better said you cuold if you'd see anything). When I tab to certain other windows the screen goes back to normal back light - I can then tab back to the other window and the backlight will be turned off again.
I have no idea what's going on and also no idea what information you need. The display-adapter I got is the AMD Radeon HD 6400M - I tried updating to the newest driver but that didn't help.
Here's a video of the whole thing: