Unfortunately, QT cannot be relied upon to open all mp3 types. You will need something better. Also Sound Jam was also my main mp3 player for a while. But they stopped developing it 2-3 years ago. the dev. team now work for iTunes! SoundJam lacks all the required codecs to play the newer format mp3's & cannot play m4a (mp4). mp3 codecs are developing all the time. May I suggest u try another mp3 player. I've found Audion 2.62 will play most mp3 formats (incl. some iTunes can't play.) It's easy to find if u search, there's heaps of them! Once you get Audion or another player, make that the default player for mp3's. Go to File Exchange control panel & add one or more of your mp3 files to the list. Then select Audion as the default player to open them. If Audion is not listed you'll need to add it. You may need to open the advanced section. I'm in OSX at present so I can't walk it thru with u. But if you still have problems, write back & I'll double-check the specifics.
I also used LW 2 up until a few months ago but I never used the launch function. I should imagine once you've set a new default player it should work fine again. I'm not sure whether it stopped working b/c of the codec issue & QT's lack of abilities or your prefs are up the putt.