It's a fact that if you try to synchronise your iPod with an empty (or different) library, iTunes will ask you if wish to delete the current content of the iPod and replace it with content from the new Library. Of course, if that library is empty, you'll end up with an empty iPod.
You could try using Manually Manage. Manually Managing an iPod means that you do not use Sync, but that you drag songs etc. on to, and off from, it. In theory, this process will not cause you to lose what is already on it.
However - and this is a crucial point: at some stage, your iPod will fail. It you manage to avoid losing it, breaking it or getting it stolen, it will eventually stop working. It will wear out. That's life. You may even decicde that you wish to replace your current iPod with a newer, more advanced model.
At that point, what do you intend to do? The only music that will appear in a replacement iTunes Library, such as the one you are using now, will be music that you've purchased from the iTunes Store, provided you've signed into the same account that you used to purchase it in the first place.
You state that you've logged in. Presumably, you mean that you have logged into the iTunes Store, but since you've also stated that you lost your password, I assume that you've created a new iTunes Store account. That will be why any music you've purchased from the iTunes Store old your old account isn't showing up.
So to have any hope of getting your music back, consider the following:
- if you had a backup of your old computer, perhaps that has your music on it. You could copy from that to the new computer. If you do not have any backup, and for music that you did not ever back up, try the next suggestions
- for music that you purchased from the iTune Store, consider trying the link to "I've forgotten my password". It may be labelled differently, but esssentially, it's the option to help you get back into an account when you've lost or forgotten the details. I'm fairly certain the Store has this option
- for music that you bought from other digital music sources, such as Amazon or Bandcamp etc., sign into the account you have with in that store and see if you can re-download the music from there. With both of those outlets, it is possible to do this. Not every store does allow it. (What a bunch of meanies they are!)
- for music that you added to iTunes from CDs, you can re-add them from those CDs to the new Library. I hope you still have those CDs
Moving forward, you need to back up your msuic. An iPod is not suitable as the only place you have your music. Nor is relying upon the store you bought it from. One store I use will only allow a re-download for 24 hours after the first download.
And two backups is better than just one.
Music on an iPod should also be on your computer. While that backs up the iPod, you should backup your computer as well, since computer hard drives do fail.
