If you are used to automatically syncing your iPod to your iTunes library, you may have lost songs on your iPod. Losing songs occurs because when you automatically sync music, a two-way sync occurs. That means if you deleted a song from your iTunes library, it will automatically delete the song on your iPod. If you want to sync your iPod without losing songs, you have to set your sync option to manually update your music. Manually updating will allow you to pick and choose which songs to add to your iPod and will never automatically delete any songs from your iPod.
Connect your iPod to your computer using the USB connection cable.
Launch iTunes if it does not open automatically. Allow iTunes to load and recognise your device. Once your device is recognised, your iPod will appear in the left column of iTunes under "Devices."
Click on the icon of your iPod in the left column. This will open up the "Summary" tab of your iPod by default.
Click "Manually manage music and videos" in the "Summary" window.
Click the "Apply" button in the bottom right-hand corner of iTunes. From now on, your iPod will not automatically sync your entire iTunes library and you will not be in jeopardy of losing any songs.