It maybe possible to tear down and verify the "belt"(if used) that drives the CD is not loose or broken, etc.. If yes, replace. However, in most cases its better to forget about any fixes or repair in general as its reached the end. Of course, check eBay or Craigslist for model# and go from there.
Can the CD player(s) on a boom box be fixed? The radio and even the tape player works, but the CD player(s) haven't worked pretty much at all. It's a major manufacturer (SONY) just not sure if it's worth the effort.