In order to get to the CMOS battery and remove it to perform a physical clear CMOS, you would have to take the unit apart, the Motherboard needs to be removed to reach it.
This is not fully recommended since it could harm the unit.
Here you can find a video of this process (not in English but for guidance could work).
After reaching the CMOS battery and removing it for more than 20 mins, you can test the BIOS recovery again.
A tip for this, make sure the .bio file is the only file in the flash drive.
Please perform the recovery to the version you attempted previously.
I look forward to your outcome with this.
I had already tried to remove the CMOS battery during an entire night but not reconnecting it with a usb key. I let the board with the CMOS battery disconnected while I was waiting for an answer here, so the battery has been disconnected for 24h at the time I tried your advices.
I did a video showing what happens when I plug the AC power right after having reconnected the CMOS battery, disconnected for 24h.
- hard drive disk unplugged since it does not play a role in this.
- DDR3 correctly plugged.
- headset to hear potential beeps (no worries, it beeps high enough to be heard without wearing them)
- bios jumper removed
- monitor connected an turned on with a VGA port instead of HDMI.
- usb key with one partition and a fat32 filesystem containing TY0024.BIO in the root directory, nothing else.
Note that this usb key has a LED which is turned on as soon as the device is used and which blinks when there are accesses.
You can see the board seems to be in some state but nothing happens with the usb key, nor on the monitor. The led behind the power button is on as if when the board is turned on. Right now, the nuc is in the state you can see at the end of the video, I am waiting for your instructions to continue.
But so far, I experienced the same before you answered and I had tried a CMOS reset by myself. From where we are now, I turned off the board with a "normal push" on the power button. Turned it back on with a "normal push", and the board was still shutting down like before after 4 seconds, without entering any recovery mode, without any screen feedback, etc. I also tried to enter recovery mode with the power button (push during ~4 seconds after hearing 3 beeps) but it does not work and there are also no beeps at all. So I removed the CMOS again to recover this weird state when you plug the power back after a CMOS reset with the usb key plugged in and let it for a while but nothing... The USB key contained junk files generated by my OSX I removed using a linux OS this time.
Thank you for the detailed information provided regarding your situation.
Right now, if you are not able to perform the BIOS recovery, I would like to recommend you to check the warranty on your device.
This can be done here: Contact Support
Please make sure you select the correct region.