LR 5.7.1 does not see and can not import Nikon D7200 files. You need LR 6 or above. You can use the free Adobe DNG converter program to convert the NEF files to DNG files and then import those DNG file into LR 5.7.1.
You need the newest version of the DNG converter program, 9.5.1.
The D7200 requires at least Lightroom 6, which is a paid upgrade.
Alternatively you can use the free DNG converter to convert the NEF files to DNGs that can be imported in LR 5.
Be aware that the DNG converter works at the folder level - you have to point it to a folder containing NEF files, and it will then convert all the files in that folder.
Thank you for your quick response. I will try the DNG converter first.