Moving tunes from iPod to iTunes

I have tried unseccessfully to transfer music from my Classic iPod to my Computer. (Computer was having some difficulties, data was backed up, drive wiped clean, all other data successfully reinstalled.) I have been trying to reinstall music from the iPod however most of the music p;urchased off the internet has not been reinstalled on iTunes. Various efforts have resulted in songs loaded from CD's are now on iTunes in a multipel of five but no internet music. I have been told I may have to purchase a special program to transfer the music. Any assistance would be appreciated.