How to transfer music. I am having problems transferring music from my pc to my mp3 playerI'm

Question

I am having problems transferring music from my pc to my mp3 playerI'm having trouble syncing songs from my computer to my MP3 player. It worked fine until last night, my boyfriend deleted the songs we had on there to put new ones on there and now when we try to put the new ones on we get an error message stating that the file has been moved, renamed or deleted. Does anyone know how to fix this delima?