So my Mac will not start since I installed the latest sierra update- it only shows the loading start-up screen for HOURS. It won’t start in safe mode or cmd v mode either. I’ve managed to get it in recovery mode and reinstalled sierra and it’s still the same, I’ve also used first aid on disk utilities to no avail. My next step (since I’m stupid enough not to have used time machine to back up my crap) is to copy my Macintosh HD onto an external hard drive using disk utility and then wipe my MacHD completely so it can restart it, and then copy any files back over to my computer from the macHD copy. The only trouble is that disk utilities keeps stopping, saying the file is too large- even though it’s only 400gb and the space on my external HD is over 500gb. I’m so frustrated as I’m not sure what else to do- and I need help! Please!