I suggest you to update the BIOS using the recovery method. It is necessary to download and keep the .BIO file in the root of thumb drive (USB) Open the NUC and remove the BIOS configuration jumper, plug the USB and turn the NUC on. The NUC will update the BIOS automatically.
The monitor needs to be plugged to the NUC and check if the video input of your monitor is properly selected.
Latest BIOS and drivers files are available at: Intel® Download Center
Details of BIOS recovery: