I don't know how much it would help, but I would try this:
- Install the latest BIOS Revision 30, and after the update, F2 in and "Load the BIOS Defaults"
- Disable UEFI Boot (or alternatively Disable Legacy Boot if you're not using it) and save/restart
I've had similar problems with NUCs not booting due to the "UEFI Boot" and/or "Legacy Boot" checkboxes.
David