Manually manage music

What exactly happens when you try to sync?

Does iTunes see the iPod?

Was the iPod previous synced to another iTunes library/computer?

Have you successfully synced from this iTunes library/computer before?

If so have you done anything like update iTunes on the computer since it last successfully synced?

Do the songs play in iTunes?

Does any media now sync to the iPod?

Do you have the right boxes checked to sync?

Managing content manually on iPhone, iPad, and iPod

Any restrictions set up on the iPod?

Did you already check this article?

Manage content manually on your iPhone, iPad, and iPod - Apple Support