I’ll bet that your son used the Clip’s format function. This command is found under Settings > System Settings > Format; he must have then selected the Yes confirmation afterwards.
The Clip+ will play music files transferred from your PC. It needs MP3 or Windows Media Audio (WMA) files, essentially, though the device does support a few other formats. The device will NOT play iTunes AAC format files transferred for the iPod, a common issue encountered, but if those files are converted to MP3, you’re good to go.
The music files can be transferred from Windows Media Player (most common use), or simply dragged-and-dropped using Windows Explorer.
Okay, here’s the last burning issue, as you mentioned: recognizing the Sansa from a different PC, most notably, your desktop. As SanDisk manufactures flash memory, it makes sense that they designed a portable player that can either communicate as a media player or a basic flash drive. The USB Mode settings may have been altered by your son.
Again, no worries, we have three choices, MSC, MTP, or Auto Detect. Out of the box, the Clip+ is set to Auto Detect. What happens in this mode is the player will first peek at the operating system of your PC, and it will try MTP first, then it will revert to MSC.
Let’s start with the music: where are your music files? The Sansa does not need a specific program to communicate with the PC. The only software needed is Windows Media Player 10 or later, if you are to use MTP mode. In MTP, many little capabilities are open to you, like secure Windows Media Audio, needed for subscription media, libtrary audiobooks, or services like Napster or Rhapsody.
So, if we can start with the basics, you have a Clip+ with no music. Do you have MP3 tracks on your computer, or are you looking at downloads, or CDs?