Q: Nearly all files in iTunes "could not be used because the original file could not be found."

When I "Get Info" for each individual song, it says the songs are located in a folder called 'iTunes Media' located in the .Trash, however there are no folders in the Trash that are even close to that name. And I checked the iTunes Media folder located at Users/MyName/Music/iTunes/iTunesMedia, but it only contains a very small fraction of music added in the last 6 months or so.

I've tried using a previously saved iTunes library (as suggested here), but to no avail.

My iTunes library is very imoprtant to me and contains (or, it did contain) 15,000+ songs, so it would be quite a tragedy to lose them all. Any advice?