Sounds like the anti virus has removed the driver software for the mp3 player from your computer. Try setting the player back to factory settings using the reset button (you will probably lose your tunes by doing this so hope you have them on i tunes or whatever software you use). Also, run the cd that came with your player on your PC, that might reinstall the driver. Uninstall, reinstall the software you use for storing your tunes (back them up first) then see if your player can be detected on another computer. XP should pick up your player as a 'device' anyway.
Stig, November 2008