Ok. Stepping back a bit.
Music files, just like files on your computer, can come in all sorts of formats. This includes mp3, aac, ogg, flac, etc. formats. The format of a file is indicated by the last 3 or 4 letters of the file name, after the period. And so the music file Take Back the Night.mp3 is an mp3 file (that is, the song encoded using the MP3 format); Take Back the Night.aac is the same song but encoded in the aac format. You can see the file name, including the file type, using your computer’s browser, or by right-clicking on the file name with your computer and then selecting Properties.
The Clip, like most players, does not play every possible type of file, although it does play many different types, including mp3, ogg, flac, wma, and wav format files. You need to check your music files, in your computer’s browser or otherwise, to see if they are of a format type supported by the Clip.
As noted earlier, the Clip does not support aac format files, the format that Apple defaults to. It is possible that, in “ripping” his CDs into music files to play on his iPod, your son ripped the songs into the aac format. If that is the case, the songs will not play on your Clip.
In that case, you could: re-rip the music from the original CDs, into a file format the Clip recognizes (the MP3 format is the most universal). Or, you could convert the aac files into a format recognized by the Clip. Of the 2 choices, the first is preferable, as, when you convert music from one format to another, you “lose” bits of data and the sound integrity goes down.
I hope this helps.