When you mean by not showing up, you mean not showing on iTunes, if thats the case, do one or more of the following:
> Restart Your Computer
> Uninstall & Reinstall iTunes
> Reset iOS or iPod (will not delete everything)
> Go to My Computer (Windows XP) or Computer (Windows Vista & 7) to see if your iOS device shows
> Restore iOS or iPod (will erase everything)
> Make sure both iOS firmware and iTunes is up to date.
Hope this helps.