If you are getting 3 BLINKS, you probably have the wrong voltage RAM.
I am not from Intel and have no idea about the seller, but blue light blinking three times typically means RAM problem. It cannot run without RAM, so that is no surprise. But if still blinking with RAM, you may not be aware of how NUC requires specific memory. It MUST be 1.35 volt memory (not 1.5 volt memory), and not ECC. The NUC does not seem to allow faster memory, so best not try speeds faster than 1600. And the most difficult compatibility issue to find documented is memory "density" which often means the number of chips per side of the DDR3L module. If you have memory with the wrong density it might sometimes work if you insert only ONE module (not two) into the upper memory slot - but that is just indication that it is not on the compatible list. I think that 4GB modules (allowing a total of 8GB) will often have four chips on each side of the module, while 8GB modules (allowing a total of 16GB) will often have eight chips on each side of the module. If you have twice that many chips, that is usually the density problem.