My screen goes blank with light still around the edges.Like you can still see the light behind the screen, this happens while you watch videos or just looking on the web. It doesn't do this all the time but when it does I half to push the power button to shut it down, then i resart it and it's back to normal. why does it do this? Is there something I can do to stop this? Or is it a warning sign?
iMac, OS X Mountain Lion (10.8.5), 2.8 GHz Intel Core 2 Duo 2 GB 800