The power LED on the Intel® NUC will blink in a pattern if an error occurs during POST. Intel NUC products that include a front panel audio jack will also produce an audible beep pattern, which can be heard through headphones or speakers plugged into that jack.
See the table for the patterns and solutions.
3 blinks (3 beeps)
On-off (1.0 second each) three times, then 2.5-second pause (off).
The pattern repeats until the computer is powered off.