iphone 5 with ios 8.1.3 loses music files and iTunes restore does not restore music files

1. I have a iPhone 5 with iOS 8.1.3 and running iTunes 12.1.1 on my computer.

2. I have the music app with 131 music files and 3 MP3 audiobooks and 3 tones on my phone.
3. One day ALL the music files and the audiobooks disappeared from my phone. when I clicked on the music icon on the home row, I only get the iTunes music store, and a message "NO CONTENT - you can download music from the iTunes Store". I have never had any issues with my iPhone or the music/books/tones files since I have had the iPhone.

4. When I plug my iPhone into my computer and view its contents through the iTunes screen, I can see all of my 131 music files, the 3 audiobooks, and the 3 tone files.

5. I backed up my iPhone through iTunes to my computer, and then deleted and reset my iPhone.

6. I then restored my iPhone from the iTunes backup. and I have the same results: there is no content visible on my iPhone, but the iTunes app shows all of my music and audiobook contents being on the iPhone.

I don't know how to solve this problem, has anyone else had the same problem? Does anyone have ideas on how I can proceed to solve this problem?

Any help would be greatly appreciated.