Are you trying to sync the iPod with a different iTunes library from the one you originally set it up to sync with? Isn't all the content that is on your Nano still in your library? If so, you can go ahead and choose Erase and Sync. Then sync all of your content, including TV Shows, back over to the Nano.
If this is a new/different iTunes library, you'll have to make it your syncing computer first by choosing Erase and Sync or restoring the Nano. Before you do that, you'll want to copy everything on the Nano to your new iTunes library first so you don't lose anything.
See this older post from another forum member Zevoneer covering the different methods and software available to assist you with the task of copying content from your iPod back to your PC and into iTunes.
https://discussions.apple.com/thread/2452022?start=0&tstart=0
B-rock