After reformatting my iMac G4 hard drive, iTunes now won't recognize my song library--what is the proper way to reload authorized music? Background:

1. I first transferred my backed-up library into the proper iTunes Music folder--whereupon iTunes couldn't see ANY of my songs. But when I navigated to the song in a folder and opened the file, iTunes played it and it would then show up in iTunes as a playable song. Can't individually click 1000's of songs, so...

2. I then used the iTunes "import" function and imported the back-up library. Now all the song titles show show up in iTunes, BUT when I select "play" an error dialogue box informs me iTunes "the original file could not be found".

3. Somewhere in there during another reload iTunes gave me an error about my music not being authorized, but I forgot the specifics of that event.

Any guidance on the proper fool-proof method for reloading an iTunes library?