ugh.
iTunes didn't name your files to mp3^, because there's no such thing. //content.invisioncic.com/y282845/emoticons/smile.gif.1ebc41e1811405b213edfc4622c41e27.gif
You need to rename those files to .mp3, like they're supposed to be.
Are there little exclamation points next to the files in iTunes? If so, it means iTunes can't find the files, because it's looking for backstreetboys.mp3, not backstreetboys.mp3^
Should fix it.
If not, remove the files from the iTunes library, rename and add back in.