Thank you for contacting Intel Communities.
I am sorry to hear you have boot issues on your Intel® NUC.
In this case, you can try updating to the latest BIOS (0046) in case you have an older version, you can use the F7 BIOS Update Instructions for Intel® NUC so you don't need to boot to the OS.
If you tried boot M.2 slots with the same results, I would recommend testing a different drive or testing the one you have on a different system that supports M.2 drives.
I hope this information helps.
Thanks Juan for the reply
I have updated my BIOS, still no luck
I am considering buying a new SSD, is the new Samsung 960 PRO compatible with the NUC?