Sometimes a grey exclamation point will appear next to songs in iTunes, indicating that iTunes cannot locate the file. How does this occur and how can you fix it?
Inside the iTunes folder, there is a file called "iTunes Library" that tells iTunes where the "iTunes Media" folder is located. (This is the folder that actually contains your music, videos, apps, etc.) When iTunes tries to access content (e.g., you try to play a song) it gets the location where the song is stored from the "iTunes Library" file and then looks for it in that location. If it can't find the file, it displays a grey exclamation point to the left of the entry in iTunes.