Q: Won't backup

Here:

iOS: Troubleshooting backup issues in iTunes

or

iCloud: Troubleshooting creating backups

I'm not getting any of the error messages described in the troubleshooting article, because I can't even get that far: the "Devices->Backup" menu selection is disabled.

Does the iPod appear in iTunes?

It did at the time I posted the previous message; I could see a list of tracks (4000-odd of them), and they all looked reasonable.  The "File->Devices" menu offered four options ("Transfer Purchases", "Sync", "Back up", and "Restore from backup"), but only the Sync option was enabled.

Unfortunately, something happened in the past hour, and the iPod no longer even boots properly (I get a very dim apple logo that stays forever).  So now I have a different problem :-)

The two symptons may be related.

Try:

- iOS: Not responding or does not turn on

- Also try DFU mode after try recovery mode

How to put iPod touch / iPhone into DFU mode « Karthik's scribblings

- If not successful and you can't fully turn the iOS device fully off, let the battery fully drain. After charging for an least an hour try the above again.

- Try on another computer                            

- If still not successful that usually indicates a hardware problem and an appointment at the Genius Bar of an Apple store is in order.

Apple Retail Store - Genius Bar                                     

Actually, it's an old classic iPod; it doesn't have a "DFU mode" AFAICT but it has "disk mode".  If I'd known about "disk mode" a few hours earlier, I would have just mounted it as a disk drive and copied the files manually.  But in the process of trying to back it up, I seem to have triggered some kind of hard disk problem.  I've put it into disk mode successfully (and the screen lights up with a message saying "Disk Mode", so at least I know the screen works), but the computer says it's a corrupted disk.

I agree, at this point it's almost certainly a hardware problem (although it worked fine at 11:00 last night!) and I'll need to take it to the Genius Bar.  Thanks for the suggestions.