Error message when trying to play music on computer states The song ... could not be used because the original file could not be found. However, my library shows how many items and the GBs used. How do I locate the files?

Question

When I try to play my iTunes music on my computer, an error message comes up and state "The song (title of song) could not be used because the original file could not be found.  Would you like to locate it?
When I click on Locate It, I cannot find where the music file may be located.  Does anyone have any suggestions?
This all occurred when I attempted to do a backup to an external hard drive.  Unbeknownest to me, the files did not copy over and do not appear on the external hard drive. 
When I open my iTunes library, at the bottom of my music list it shows how many songs and the GBs, so it appears that the files are still there; however, cannot be located.
Thank you.

Answer 1

Hi angela dfromtx,
When tracks in iTunes display a it means the file cannot be located; it may have been moved or deleted. You'll have to locate the file manually if it is still available. For more information refer to the following article:
iTunes: Finding lost media and downloads
http://support.apple.com/kb/TS1408
Alternatively, if your media was downloaded from the iTunes Store, you may be able to download it again free of charge:
Downloading past purchases from the App Store, iBookstore, and iTunes Store
http://support.apple.com/kb/HT2519
Thanks,
Matt M.