You need to do three things: Clear CMOS, reinstall the latest BIOS via the Recovery Method and reset the BIOS configuration...
- Normal instructions for clearing CMOS can be found here: Intel NUC Clearing CMOS. I personally do not think much of this method, however (it is inconsistent). You can try it. If it doesn't work, use the more-effective method, which requires you to unplug the CR2032 battery from the NUC's board for 15 minutes. Unfortunately, the battery connector is on the processor side of the board and you will need to at least partially remove the board from the chassis to access it.
- Instructions for BIOS Recovery can be found here: Intel NUC BIOS Recovery Update Instructions. I highly recommend using the Jumper-Based method; it does a better job than the Power Button Menu method.
- To reset the BIOS configuration, do the following:
- During POST, when the splash screen appears, press F2 key to enter BIOS Setup (the Visual BIOS program).
- Press F9 (followed by Y) to clear the BIOS configuration.
- Press F10 (followed by Y) to save this change and then exit BIOS Setup.
- During the subsequent POST, again press F2 key to enter BIOS Setup.
- Make any changes that you absolutely require/desire in the BIOS Configuration (Boot Order, SATA Mode, etc.).
- Press F10 (followed by Y) to save these changes and then exit BIOS Setup.
Hope this helps,
If you cannot POST after clearing CMOS nor will BIOS Recovery activate, then it is completely bricked and you have no hope of recovering the board. In order to setup an RMA, you need to contact Intel Customer Support directly. Here is contact information, by geography:
You can also try using the Intel Customer Support Chat Service, but understand that this is English-only and subject to 9-5 working hours in Pacific TZ.
Hope this helps,
P.S. In the RMA process, Intel will send you only a replacement chassis (with board). Consequently, you only want to send back your chassis (with its board). Keep your drives, your memory and the power supply to use with the replacement chassis.