Help! 2011 macbook crashed suddenly. No warning signs. It went into a reboot loop. Since then I have spent a whole lot of hours trying to diagnose the problem and going nowhere. Can't get to safe mode. Can't get to OSX recovery. Can't get to diagnostics. These options lead to a boring grey screen, same one I get to if I boot without pressing those keys. Tried booting from a OSX thumbdrive. Same grey screen. Option D does get me to internet diagnostics. Macbook passed the basic test. Hardrive works fine as a target disk over firewire. I reset the NVRAM. In single user mode I ran fsck and "the volume appears to be ok". However a lot of the boot messages that come up prior to that don't look terribly healthy. Is it possible that that hardrive is permanently damaged? If so why would it work fine as a target disk? I don't get it. Is it possible that the hardrive can become instantly and irrevocably corrupted? Can I duplicate it (ie clone it to an external hardrive via target mode) format the drive and then copy the clone back over it ie so all the software and files return intact? I've been using macs for many years and never seen one suddenly fail like this.