I have had this issue recently where sometimes, not always, then I shut down my computer (either via the Case Button, or vie Start Menu) the PC shuts down, and then immediately turns back on. Then, if I shut it down, it stays shut down. This doesn't happen every time. I don't know what you possibly be causing this issue, so I've done Zero Troubleshooting so far.
I have a Gigabyte Z87-HD3, i7-4770 (non-k), Gigabyte GTX770, 16GB DDR3 Kingston Beast Series RAM, Samsung 850 Evo (250GB) + WB Black 1TB, Running a relatively fresh Windows 10 install (about 2 Months)
I've read that people with Gigabyte motherboards had some kind of Gigabyte utility for charging via USB when shut down. The anwser then was to uninstall that, BUT I do not, nor did I ever, have any Gigabyte Utility installed on this OS installation.
Wake on LAN
is enabled?