I have a late 2015 5k iMac with a 4ghz i7, 8gb ram , AMD Radeon R9 M3995x 4gb and a 500gb ssd running MacOS Sierra. The computer shuts off randomly and if I try to turn it up with the power button it doesn't turn on, I have to unplug it, wait a few seconds and then plug it in. I took it for service and did not showed anything, brought it home and for about 3 weeks or so worked perfectly, once again started to fail with the same problem, this time I took it to Best Buy since the computer is just 1 yrs old and I bought apple care, They ran all the diagnostics and the computer did not showed up anything again, they reinstalled the OS and I brought it home, after a couple of days I upgraded to Sierra version 10.12.1 and a couple of days later I still have the same problems. Im a photographer and its annoying having this issue with a new computer and having to deliver work in a timely manner to my clients. Does anyone has any clues of whats the problem?