I assume he installed some software to make him MP3 player compatible with your PC . You can do a few things. You can find out what the process name is that is causing you the trouble.

1) You can do this by opening Task Manager and looking at all your processes and figuring it out and then going and turning off the service (if there is one) found in Control Panel/Administrator/services . Task Manager is in C:\Windows\System32\taskmgr.exe or you could just hit "ctrl ALT DEL " simultaneously.

2) Or after you have found the process, find it and uninstall it either by going to the folder or going to Control Panel/Remove Programs .

3) Get "Hijack This" and find the registry entry that causes it to run and just delete it. http://www.tomcoyote.org/hjt/

You need to know what the process or name of the problem is and the process to delete will have a " HKLM\...\RUN " right before the name of it and that would be the one to delete. This is dangerous way to do it , though because you could potentially screw your whole computer up if you are wrong. I advise backing up your registry before attempting this or making sure you have a Plan B if something goes wrong.