My quick checks are:
Try a new cable (a kink can stop it from working)
Try a different port (rarely one goes bad)
Try rebooting the computer (the Microsoft fix)
Try a different computer (see if it is recognized)
Then follow the articles above.
If you don't get it resolved:
- What error codes or messages do you get
- What version of iTunes are you running?
- What version of iPod Nano are you using? https://support.apple.com/en-us/HT204217
- What version of OS X are you using?