Channel switched to "L", but you still hear the voice in multiplex songs.

You need to reinstall the codecs for "mp3" files.

Download and instal this codec pack: http://codecguide.com/download_k-lite_codec_pack_mega.htm

And this: http://codecguide.com/klcp_64bit.htm 

(There are many confusing banners on that pages, find and click on "Mirror 1" or "Mirror 2" to download the files.)