Windows Media Player album art display?

This isn't the WMP album art question I've seen six thousand of, I know how to paste album art and whatnot. Until last night, WMP displayed my album art just fine next to my albums (in the "songs" view). The next time I opened it, there was no album art, and not even the option to "Paste Album Art Here." Any help would be greatly appreciated, b/c my library is unbearably boring now. Thanks!