I have a 2013 model - spec in sig. Today I switched on my MBA as normal and got nothing - straight into the OSX Utilities screen. Tried choosing a startup disc - nothing. Rang Apple - repaired drive permissions etc and still got the same. It was as though my drive was completely empty! They just advised me to reinstall OSX cleanly!!! Some solution that is! Tried a Time Machine restore from my TC - it finished the restore and then did the same thing again!! Tried connecting an external drive to boot off of an image - it wouldn't even recognise the drive. In the end I had to completely reinstall Mountain Lion from scratch then use migration assistant to get all my data and apps back. I then upgraded to Mavericks fine. The only thing I did was the recent firmware update to the MacBook Airs - but that was 2 days ago and it wood fine until today!! Any ideas why this happened?? It was as though suddenly I had a completely empty drive all of a sudden!! Rather worrying!