Hhmmm, the "POST Operations Unsuccessful" message is sometimes an indication of a problem with memory initialization (i.e. the system is not able to initialize it using the settings in the BIOS configuration). This may be an indication of a memory problem (bad DIMM possibly) or it may simply be an indication of a problem in the BIOS configuration.
As a next-step, I would suggest that you try upgrading the BIOS to the latest available using the recovery method. Instructions are provided here: Intel® NUC BIOS Recovery Update Instructions. When they talk about the "Recovery BIOS", they are simply talking about the latest BIOS.
Once you have the BIOS installed, go into BIOS Setup and use F9 to restore the configuration to defaults. Then, make any changes to the configuration that are absolutely necessary for your hardware or system design (boot order, etc.). Save settings on exit.
Hope this helps,
There are two ways to recover to a new BIOS.
1. Put the latest BIOS .BIO file on the root of a USB 2.0 flash drive. Make sure that only (1) .bio file is in the root of the flash drive. Open the NUC, remove the yellow recovery jumper on the board located next to the SoDIMM slots. power the unit on with the flash drive plugged in and wait for the unit to POST. You should see a message saying the BIOS will recover in XX seconds. Just let it go and it should start the BIOS update. If it does not display the recovery message, try using a different flash drive. When the process is finished, power off remove the AC adaptor and restore the yellow jumper back to its original position.
2. Same steps as the first option as far as the BIO file on the flash drive. With the unit off, press and hold the power button for 3-4 seconds until the LED changes to orange, then let go. The system should boot into the Power Button Menu. Select option 4 (BIOS Recovery).
After either of these is done, you should see a message saying to power off and remove the AC adaptor. Do this, wait about 10 seconds then plug back in and power on. Press F2 to enter the BIOS and press F9 to load BIOS defaults. Then press F10 to save the settings and you should be good to go.
Thanks Scott and Mitch for pointing those update methods out.
I had no success with the power button method. I plugged my earphones in the jack waiting for those 3 beeps but never made it work.
So I tried the jumper method.
What struck me was that the jumper was on pin 2 / 3 (with the RAM towards me) which I believe is the "Lockdown" mode.
I'm not sure what it implies but it may be why I could not update using conventionnal F7 method ?
I removed the jumper, plugged my usb key with the BIOS 42 and powered on.
The BIOS update worked like a charm, it was nice to see it work after all those fails.
I put the jumper back but I tried to place it on 1 / 2 in "Normal mode" but for some reason I wasn't prompt to access to the BIOS at the Intel nuc splash screen anymore.. tried 3 times, no success with the F2 key. After moving the jumper to 2 / 3 in lockdown, I was finally prompted with BIOS access. I put everything to default even tho I didn't change much in BIOS 28.. just the fan speed.
I'm happy to say that Ubuntu 16.04 (previously 15.10) now correclty power off at shutdown !
I may have a stability bug with the kernel boot parameter i915.enable_rc6 (power saving) but that's another story unrelated to the BIOS I hope..
Thanks everyone for your help.