One tip when posting on a forum is to put your question in the body of your message, rather than in the title. There isn't much room in the title and part of your question was cut off making it difficult for anyone to answer.
I have grey songs as well that my niece put on my ipad when we were new using her Mac through the air. When I was last at the Mac store they said the only way to get rid of them was with her computer.So I have to wait till I'm back in her province.
Sorry if I hadn't been more specific, those greyed out apps can't be played or accessed on your device because its been moved or missing
You have to manually point each grey file to where it's physically located on your PC.
HTH