1. After momentary depressing the Power Button, is NUC powering ON? Can you see the "Intel NUC" logo?
2. If you see the "Intel NUC" logo, click repeatedly on F10. Is your NUC booting into Boot menu?
1. I suggest you to reinstall Windows using the following method:
2. Please prepare your installation media (you need 8GB – 32GB USB stick), using Microsoft Media Creation Tool. This will install the latest version.
3. Your bios should be set to default settings. Enter bios (press F2 during boot) and then press F9 (Y) to set defaults and F10 (Y) to save settings and exit.
4. With the installation media inserted into rear USB slot, power ON your NUC and repeatedly press F10 to get Boot Menu.
5. In this menu, choose UEFI option of your Installation media.
6. Follow this tutorial to continue with installation.
7. In para. 9 you may enter Product Key from the Microsoft Distribution you bought .
8. Skip on para. 14 and continue in para. 15. Important, do not format drive where you want to install Windows, rather delete all existing partitions from this drive, till you see one unallocated space.
9. Press Next and continue with the installation.