Press repeatably F2 key during boot, to enter bios.
In bios, press F9 confirmed by "Y" to set bios to default settings.
Press F10 followed by "Y", to save settings and exit to Windows.
If the above steps, will not help, please open NUC cover and check if LED cable is connected. The cable should be connected on both ends: to the LED panel (the upper connector) and on the other end to the board.
