If you've tried the standard fixes, go into your Internet Control Panel. Switch to the Advanced tab and click the "Helper Apps" icon.

All you should have to do is make absolute sure that there is no file type that considers Limewire as it's helper app. Part of Limewire including a "Player" is that it makes it a "legitimate" helper app and can override your system prefs.

I don't know how it happens, but Limewire will sometimes decide it's your new .sit opener or your new .mp3 player. g/l