What does this mean? "((•))" Downloaded song and played it for months. It then stopped playing and the ((•)) symbol appears to the left of the song title.

What does this mean, and how can I get may song playing again?
That symbol indicates the "song" is an online stream rather than a file downloaded to your computer. This happens if you add a URL to your library rather than downloading the file and adding that.

So you must have been streaming the song each time you played it and now the stream has been turned off. You obviously need to find and download an actual copy of the song file to be able to play it again.