ipod nano

iPod synchronization is one-way – from a master library on a computer, to the iPod. The system isn't set up to let you load music from one computer, attach the iPod to another computer, and copy the music to it. Or to load music/video content from multiple computers onto the same iPod at the same time.

I can think of two reasons for this. One technical, to make the synchronization easier (and the model conceptually easier to understand). The other, to placate the record companies, who insisted on trying to force unwanted DRM on portable music players even after the RIAA lost a court case against the maker of an early MP3 player. An iPod that made it easy to transfer music from one computer to another (as if it were a USB flash drive) would have been just the thing to attract the negative attention of the record companies.

What the dialog is telling you is that the last computer that loaded this iPod was named "John's MacBook Pro" and that since you are now using a different computer to load the iPod, that's going to wipe out everything on the iPod, and load the iPod based solely on the music, movies, and TV shows selected on the new computer: your iMac.

Your choices are:

1. To allow the deletion of all of the iPod's old music and video content, so you can load content from your iMac, or
2. To decline, keep what's already loaded, but not be able to load anything more.

There may be third-party applications that can get inside the iPod's hidden media library, and transfer stuff from the iPod Nano to a computer, but neither iTunes (pre-Catalina) nor Finder (Catalina and later) will let you do this.

It obviously believes that the iPod Nano was last synchronized with a library on "John's MacBook Pro" – or it would not be showing that message.

If that name is coming from flash storage somewhere on the iPad Nano (as seems likely), and it's not correct, that raises the question of whether the iPod Nano is experiencing some sort of hardware or software failure that keeps it from consistently remembering its connection to your new computer.

One thing that comes to mind – even though it seems like a remote possibility: You can only rewrite a sector of flash memory so many times before it stops accepting new writes. Sometimes when a sector of flash memory "burns out" (so to speak), you can still read the old contents; you just can't change them.

Could this have happened to some of the flash memory on your iPod Nano? If it is unable to accept new writes, then there might not be a good way to change the song selection on the iPod … even if you could keep charging the iPod again and again to play the current selection.

You could try restoring the iPod to factory settings. If the problem is due to a software glitch, a reset followed by a reload might fix the problem. On the other hand, if the flash in the iPod Nano is "burning out", a reset might be just the thing to brick the iPod for good.

Restore your iPhone, iPad, or iPod to factory settings - Apple Support

I don't believe Apple offers hardware service for iPod Nanos any more.