"sync ipod" is grayed out

An iPod can only be synced to one iTunes library at a time. Since that iPod was used with another computer's iTunes library, your new iTunes probably still considers the other library to be synced library, and will not allow this library to sync. You can manually add content (drag and drop), but not sync automatically.

Since all of your content is now on your new computer (there is nothing that is ONLY on your iPod), you should just give your iPod a fresh start by using the Restore button in iTunes. This will erase the iPod and initialize its software. Then set up syncing as desired, when iTunes asks if you want to sync the iPod to your new computer's iTunes library.

Alternately, you can go to the iPod's Summary tab in iTunes. There is an option (a checkbox) that says +Manually manage music+. It is probably checked currently. Unchecking it and clicking the Apply button bring up a message warning that the iPod will be erased and synced to the current iTunes library. This will erase the iPod's current contents and sync it to the new library. Since that's what the Restore button will do anyways, you might as well just do a Restore.