My Ipod doesn't sync songs anymore, can anybody help me out with this?

Hi all. Recently i did a Recovery on my computer and that wiped everything clean off of my computer, including the Itunes program that i downloaded. And now, every since i downloaded Itunes again, it won't sync songs into my Ipod anymore. When i would download a few songs into Itunes, I would press on the sync button a message comes up saying that my ipod is synced with another Itunes library and can only be synced with one at a time. This won't let me transfer the songs onto my ipod. When i tryed to sync my songs again another message pops up saying to 'erase and sync'. Meaning that in order for me to sync the new songs onto my ipod, then they are gonna erase all of my existing songs that is currently on my ipod already! I don't wanna do that. I thought about restoring my ipod but i'm afraid that that would erase all of my songs off of my ipod as well. What do i do? Help would really be appreciated. Thank you.