PLEASE revise the page Getting-started-with-the-rRF52-Development-Kit to include
"confirm that the nRF52 DK has appeared as a removable drive named "JLINK"...
If drive is not found verify that the USB cable is NOT a "power only", 2 wire cable since this has no data transport and cannot be used.
LED LD5 near the power connector should blink 5 (?) times quickly and then remain on. If it continues to blink the cable is not acceptable.