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Thank you for contacting the Intel community.
Please bear in mind that Intel hasn't validated these operating systems with the Intel® NUC but there are reports by owners of the Intel® NUC that this operating system works ok with this NUC.
We recommend you use the latest kernel. If you need assistance with Linux* on Intel NUC, check your distro's website and forums for peer assistance. I suggest you to post your question here:
Also, you can wait for somebody else to post on this thread to help you how to configure the BIOS on the Intel® NUC using Fedora.
Researching reports about installing Linux on your NUC model indicated that most versions of Linux have some kind of problem on it, such as graphics or wi-fi connection. The most reliable one and most likely to work perfectly straight after installation was Ubuntu.
I wonder if it is using the USB to boot instead of the optical drive because it cannot find a valid OS installation to boot with on the optical drive. Like the old days of 1980's PCs where it would ask you to insert a floppy boot-disk if the hard drive boot was missing or corrupted.
Also, when you made the changes in the BIOS, did you Apply them before exiting the BIOS? I don't mean insult by asking that - even I get caught out by not Applying settings changes sometimes.