I had this problem when my computer died and i wanted to load all of my ipod contents onto my new computer. iTunes will want to reformat your iPod and erase everything there and force you to start over. The only solution I could find was to buy some software that would copy the songs off of the ipod and load them into iTunes. Then it would reinstall the songs back on the iPod again and everything was in sync. I used a program call CopyTrans. I think it was around $20. I figured it was cheaper than trying to manually try to rip and reload thousands of songs. Good luck!