No matter how often they tried recalibrating the sensors they could not pick up on the ship responsible, or the intruders on board. In fact the only confirmation that there were intruders on board were the corpses, cut off emergency comms requesting back-up, and the rampaging sentient creatures made out of some strange energy-fire that was resistant to all fire-retardant chemicals. In fact the only way to stop them was to open that section of the Narada to space and vent them out into the black where the flames extinguished and they "died’ out.