After manually downloading my music to i tunes, how come some files are missing ??
When tracks in iTunes display a it means the file cannot be located; it may have been moved or deleted. For this issue, we will need to refer to the following article:
iTunes: Finding lost media and downloads
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
Retrieving data ...