If you copied the entire iTunes folder to the external drive then press & hold down shift as you hit the icon to launch iTunes and keep holding until prompted to create or choose a library. Click choose, browse to the iTunes folder on the external drive, and open iTunes Library.itl.
Otherwise see Recover your iTunes library from your iPod or iOS device.
Thanks for the prompt help, I tried it but still only the purchased music appeared in my library. I forgot to note that since I deleted all the original iTunes files including the iTunes Library.itl, what I did was just copied the new iTunes Library.itl in my new location together with iTunes files after launching it. I thought that by duplicating it would normalize everything but it did'nt. Maybe it has something to do that the new Library.itl which is not the same with the old and original .itl file. Is there another way to solve this without going through the whole process of adding and syncing my entire music files and apps again? Thanks again for the help!
Elgin Santiago wrote:
Is there another way to solve this without going through the whole process of adding and syncing my entire music files and apps again? Thanks again for the help!
Check the sizes of all the .itl files you can find on the system or any backups. Perhaps an 'original' is still there to be found. Otherwise you'll have to rebuild, either by recovering information from a device, or importing what media you have into the new empty library.