iMac Late 2013 purchased 2015. 16gb RAM i5. This morning screen just stayed black. Would not light up. Tapped the keys, pad nothing. You can hear the drives going, its on. Just would not wake up. Had to tap the power button on the back a few times...it worked and I logged on. Decided to try and reboot. Stuck. iTunes wouldn't respond, Mail, App Store, Notes, Calendar all stuck won't quit. Forced quit all of them then Finder unresponsive. lol Ok so I shut it off with the power button. So my first hard crash with Sierra.... Anyone else experience this?