If you are on a Mac that has a NVIDIA gpu. For example, my Macbook Pro mid 2010 has a NVIDIA GeForce GT 330M. You have found you might get an black screen with your keys still lit up every so often that you can do nothing about besides rebooting. This is because you have a NVIDIA gpu. The only way you can stop this form happening is if you download gfxCardStatus from here. This app not only allows you to see what gpu you are using, but allows you to switch between them. So I have gfxCardStatus make it so my laptop doesn't use the NVIDIA gpu, but the build in Intel one that all Macs come with. Just download the app and make the menu drop download like this and have Integrated Only checked: sources: http://forums.macrumors.com/showthread.php?t=1182104 https://discussions.apple.com/thread/3191083?start=0&tstart=0 P.S. You are not alone Apple needs to fix this!