I purchased a NUC5i3RYH back at the end of February and have had been running Ubuntu 14.04.2 since (aside, with a myriad of graphics driver related/suspend issues and the bluetooth not coming out of suspend sometimes).
I updated to the latest BIOS (0247) on Monday 1st June, a few days ago. Previously, I was on the original Dec 2014 BIOS (either 0132 or 0130 I can't remember which).
I left the machine suspended earlier today and came back to find it would not respond to the power button being pressed (still blinking orange). After unplugging, the power button is totally unresponsive and the machine will not power on at all. The green NIC light at the back it still lit up though, so the PSU is working.
It seems like this is a bit of a known issue with the NUC:
I haven't tried removing the CMOS battery and frankly, don't really see why I should need to get a screwdriver out to switch a PC on in 2015 - particularly on a brand new machine under warranty. I need this machine for work and cannot really live it with being unreliable or being apprehensive every time I press the power button whether I will see the BIOS splash or not...
So, it's going back and I will try and get a refund (or otherwise I'll donate it to the Linux kernel graphics driver guys as it might help).
I'm really sad and disappointed - I loved the idea, size and compact power but this design flaw renders the NUC useless. I've lost complete confidence, particularly when I find that this issue has been reported for quite some time (6 months back) and no real solution found. If I had known how much trouble the NUC would be, I would never have purchased it. I would like other people considering the NUC (particularly with Ubuntu) to go in eyes-open.
(OK, fine I bought cutting edge hardware but ironically Linux support actually worked perfectly when I first ran it back in late Feb, and has progressively got worse to the point of killing it!).