Music is greyed out and won't sync to Iphone4S

Good day everyone!

I have a problem that's been bothering me for a while now.

as you can see, my Iphone is updated with the latest version.

My problem begins when I try to sync music to it. Take note, that I had no problems syncing music to it before. It just happened. I was able to sync only few into it, but the rest won't. Also, I sync my music manually.

^An example of what is happening.

And I'll just add in this info because it might be one of the causes

Lastly, I tried restoring it, but nothing changed.

Hope someone could suggest me how to fix this problem 😀