Why does a back up take hours and I frequently get error messages - i.e. the back up was cancelled - particularly annoying when I have left it to run overnight and come down in the morning to discover it was a waste of time and electricity!
Backups to iCloud take forever, but usually when you backup to iTunes it should work. Try going to Settings>iCloud>Storage and backup> and turn backup off
Since you say yo have a 2G iPod yo must be backing up to iTunes. See:
iOS: Troubleshooting backup issues in iTunes
Retrieving data ...