Try opening with VirtualDub. See
http://www.virtualdub.org/
If file opens then export to AVI using VirtualDub.
Does the file open by double clicking in Windows? If not you may need a codec from Microsoft for your Nikon Camera. Just search Microsoft camera codec. See
https://www.microsoft.com/en-au/down....aspx?id=26829
The above codec pack is from 2014 and supports up to Nikon D7100. May work with yours. I used this codec pack on Windows 7 but I think Windows 10 includes it as I have not had to install it under 10 for my old Pentax and Canon.
VirtualDub is a great program that does capture as well.