For some reason my USB3 external HD wasn’t being recognized by my NUC. I had a very old BIOS version, so I tried updating it, which solved the problem. Here’s how:
Search for the latest bios:
In my case, it was this one. Download and save the .bio file in an USB key.
Open your NUC and look for the BIOS security jumper:
Change the jumper’s position so the F2 for accessing the BIOS will work:
Now boot the NUC with the USB key (with the .bio file) connected and press F2 to get the BIOS. There, press F7 to update it:
Select the .bio file:
And start the update:
After that, my USB 3 external hard drive was recognized again.