I have a mid-2012 MacBook Pro. It has the latest update before Yosemite on it, at least the last time it was working... Two days ago I knew I was going to be gone for a day so I shut down my MacBook Pro, which was working 100% perfectly, unplugged it because it had 100% battery, and left it on my desk where it always sits. Today, I can't get it to start up. It does turn on, and the light on my charging cord tells me the battery is still 100%, but after about 20 seconds of trying to start up my files it unexpectedly shuts off. There is a loading bar, which I have seen in another thread here is something with Yosemite, so I'm wondering if maybe it's trying to do something with the update and therefore can't start up my files. I am currently running the hardware test on the advice of a different thread (I held down D while starting up), but that thread had a slightly different problem than mine, I'm pretty sure. I'll say what the results are when it finishes. I do have a back up, but it is a few days old and I would prefer to not have to reset my stuff. I did also make an appointment at an apple store, but the earliest I can get in is next Saturday, and I really can't afford to go a week without my laptop in my college classes.