Q: Almost all of my iPod touch (fifth gen) music library has gone???

At first most of my music library had red rings around squares next to songs, after researching one of the fixes was to do a sync on the computer, I did this but now they have all just gone. I have the songs that originally didn't have a symbol but ones that had a symbol are gone, how can I get them back? Or anything! I was listening to the songs that have gone just yesterday!! Quite annoyed! I started with 1007 songs and now have 311!    

Also, when I plugged my ipod into a computer the songs that had a symbol on my ipod had an explanation mark next to them in itunes (11.1) ipod runs latest version of ios 7