iPod won't detect iTunes on ext Hard Drive anymore

I have a 3rd Gen iPod Touch (32GB) and configured my iTunes to an external Hard Drive since my computer hard drive is limited. Set up was fine, as explained on this forum site, and everything worked well for a few months. However, suddenly, my iPod doesn't recognize the iTunes in my external Hard Drive any more. It actually defaults into my C: drive on my computer, in My Music even though the configuration is set up for the ext hard drive (D: drive), not my internal C: Drive.
I checked the settings and I still see the desginated iTunes in the "D" drive, which is the drive for my external hard drive (nothing has changed). I'm using the same ext hard drive and the exact same computer, a Windows PC notebook. I tried to do the set up all over again, but no luck, it still set on the "D" drive where it belongs, but won't recognize the iTunes library on that drive. Any ideas on what went wrong, and how to fix??

That's probably because the basic iTunes files are in the Program Files folder on your C drive. And the registry entries likewise point to it. Many programs, iTunes included, default to drive C or your "Win Drive" even though you direct it to drive D or another external. There are probably files from iTunes installed on drive D but I think you'll find the core files and folder are likely on drive C.

It's best to reinstall iTunes and this time direct the install to your C drive. If that drive is too small, you can always get a larger one.

Regards.