Why does "!" appear next to song titles when attempting to copy? Why are songs duplicated in Music Library?

Thanks for your reply, Chris. Right now everything seems to be going OK. Made a "iTunes Media" folder on the external drive; went to preferences - advances - in iTunes and directed that a copy be made. It's been running now for several hours, so I won't know the final outcome until probably much later. But what I have noticed on the Library >Music screen, almost all the songs have the "1" next to the name. Also, there are several titles that are listed several times (duplicates/triplicates) that are from the same album. How do I clear this up (once the copies are OK, and they prove to be correct)? Do I need - somehow - to create another iTunes Media folder for the main listing of music? If so, how do I do that?

Thanks for all your help

Thanks. I'm going to let this finish copying and see what happens. I'll do as the link suggested, but I'm still concerned about the "!", and the duplicate songs. How do I clear that up?

MOST of the files transfered to the external hard drive. Also, I have the 'original' files still on the 'main or primary' external harddrive. However, when I go back to the primary harddrive, and attempt to play a song, the dreded exclamation point appears asking if I want to locate the file. Is there anyway to prevent this besides going through each individual song, searching the primary harddrive and ok-ing the "get info" choice? Also, it still shows 35,000 songs. When selecting "duplicates" should I delete all that appear? Will doing that delete all in the music library? I really am confused about this and apreciate your help.

Thanks

Through "preferences", "advance" drop down I go to "iTunes Media folder location", click "change" and find the external harddrive where all the songs are contained. Click OK and attempt to play the song. Each song I click on, an explanation point shows and states: "The song (title listed) could not be used because the original file could notbe found. Would you like to locate it?" Clicking the "Locate" button pulls up the external hard drive where all of the music folders are located. I find the album folder and click it. All of the songs from that album appear, and I select the song that I originally attempted to play. Once the song is clicked, it is "reconnected" to the music library. Is there a way to reconnect all of these songs/titles (by different artists) in mass?

Thanks again

P.S. Was able to eliminate all the duplicates (YEAH!)