why is my itunes deleting albums from my ipod classic when I sync

I noticed my ITunes lost albums that where there. I synced 1 of my classic Ipod, and it deleted the albums from my Ipod. I then uninstalled and reinstalled ITunes, all my music popped up, I synced a 2nd Ipod classic, same thing happened, it deleted the albums from my ipod again.... I have one left.. and I am not syncing... HELP!!!!

THANK YOU!!