Unfortunately, that often means the hard drive in the iPod has become faulty. You can try putting it into Disk Mode
If it goes into Disk Mode, try connecting it to the computer to see if it is recognized in any way. If iTunes sees it, you can do a Restore, which will erase (reformat) the hard drive, install the latest software, and set it to default settings.
You may also be able to get information by putting it into Diagnostic Mode