Does iTunes see the iPod?
Was the iPod previous synced to another iTunes library/computer since you last synced to this computer again?
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 like apps now sync to the iPod?
Do you have the right boxes checked to sync?
iTunes: Syncing media content to iOS devices and iPod
https://support.apple.com/en-us/HT201253
Try syncing using the manual method
Managing content manually on iPhone, iPad, and iPod
https://support.apple.com/en-us/HT201593
Last, backup to iTunes and restore from that backup