Macbook air black screen

I got a new macbook air (1 month old). When my screen times out sometimes the user login page doesn't appear. Instead I get a black screen. So I figured a temporaily way of fixing that problem. which is to flip down the screen and flip it back up after 5 second. My user login page will the appear. But my concern is what might be causing this issue? My OSX version is 10.8.5 Any suggestions?