Mac OS X / iTunes not recognizing iPod?
It may be a format issue. In non-iOS products, there's something called a format. If you originally synced it to a PC, then it won't sync with a Mac (and vise versa). The only way to sync it with the other computer is to format it. This (hopefully) won't be a problem because of iTunes in the cloud, which syncs your music throughout your computers. I hope this helps!