hi macarong, and welcome to the forum ! i'm glad you got your mp3 problem sorted, i would have been so worried if it happened to me ! i never use my prs 700 for listening to mp3s, i have other devices which are better suited to that and i don't want to run the batteries down.
take a tour around the forum, you'll find a lot of great information and helpful people here.
don't hesitate to ask questions.