Nobody can help you unless you supply more information. For example: when did the problem first start and after what operation; was/is the artwork embedded or pointed at an image file; what are your settings in Prefs/Tags (1)/Artwork storage; what appears when you right-click a file and choose edit and then artwork tab; does the artwork show up when the file is looked at in an external tag editor like Kid3 or Mp3tag; --etc.