I have a 2012 Mac Book Pro, here is the issue I recently upgraded to Yosemite about 2weeks ago and my machine was running better than it ever has. I recently did a security update not sure if that had anything to do with my issue. I turned on my computer and it was a blank screen I could hear the internal system working as normal but just a blank screen. Then a grey screen came up with a black bar and the apple logo then it was asking my if I wanted to reset my password. I have tried restarting holding shift, I have restarted holding the option command button down and I have rest the PRAM and still nothing. I need to recover some things from my desktop but afraid that its all lost. Can anyone give me some tips on what to do next?