Re: no music
Never seen that error before, all I can think is your sound is knackered, your mp3 codecs are knackered(may not be used) your game is knackered. So here goes:
Try verifying your game cache files.
Try posting your DXDIAG log to do this, start, run, type DXDIAG, save all information then copy and paste in here.
Can you play any other Source games?