My iPod nano completely eliminated all 214 songs from my music, leaving just the songs I recently purchased (9). How can I get them back? I've tried redownloading them but it didn't work.

Question

My iPod nano completely eliminated all 214 songs from my music, leaving only the 9 songs I last purchased.  When I try to sync, I get a message, "cannot be synced because the iPod cannot be found." 

Answer 1

When you say "account," do you mean your iTunes library, because your iTunes library is what is on your computer?  Your iTunes library does not have an email address.  An account that is related to iTunes is your Apple ID (which is an email address) and you use it as your user name to sign in to the iTunes Store, to make purchases.  Changing your Apple ID will not make songs disappear from your computer's iTunes library.
If you had an Apple ID and used it to make song purchases from the iTunes Store, and then started using a different Apple ID, you should be able to re-download the songs purchased with the old Apple ID.  In iTunes, sign in to the iTunes Store using your OLD Apple ID (and password).  That may not be your current email address, but Apple uses it as your user name, so it does not matter.
On the iTunes Store Home screen, click on Purchased under QUICK LINKS.  This takes you do the Purchased screen, where you can re-download previous song purchases (for that Apple ID) at no cost. 
NOTE:  If those song purchases are from more than a few years ago, you may also need to authorize your computer to play (and sync) songs for your old Apple ID. 
For songs that were not purchased from the iTunes Store, if they are also gone, you cannot get them back unless you have a backup (or they are still loaded on your old iPod).
If that's not what you mean by "changed the email address on my account," please post back with more details.