You need to rebuild your desktop, on start up if I remember right hold down the command key (apple) and the option key while pressing the start button and hold till a little window pops up asking if you would like to rebuild your desktop. Click OK. For more info search the help center for and search for something like "startup keys."

Else if rebuilding doesn't work use the file exchange control panel and select mp3 and make sure that your proffered program is selected to open them.

You should not have a problem burning them (depending on what your using) as long as they have the .mp3 ending.