Hi MarcusW,
perhaps a BIOS recovery could help you - if you know which BIOS you have in your NUC, you can download the corresponding .BIO file from the Intel NUC driver download center, put it on the USB flash drive and reinstall the BIOS to see if the NUC will boot.
It might also be the case that the bootblock on SSD was corrupted somehow - you could try to fix that with Windows recovery disk (for which you again need a USB flash drive and another PC where you can make that recovery disk).
Let us know how it goes.
/HarveyV