Why can't I import MP3 files into iTunes on my Mac?

I've downloaded a bunch of MP3 files on my Macbook over the past like few months-ish and they've all been fine, but recently (like within the past three weeks or so) i cant move new MP3 files to Itunes/Music. Usually they open automatically when i double click the file and open in Itunes/Music, but now the picture where the album would be is just white and looks like a regular file instead of the album cover. I've tried dragging the files into playlists, Using the import command, clicking open with Itunes/Music and nothing works. I can play the files in quicktime player still, but not Itunes. Is there any way to fix this?

[Re-Titled by Moderator]