Glad you got the audio issue sorted out.
I sent an email to Valve and will check with our tech team on Monday to see if anyone has ideas what could be causing the problem you're having. The issue with access violation errors that others have reported are supposedly due to the activation system we use, and since the Valve versions are not wrapped with that activation system, that's why I don't think it's the same problem. Well... either that or the errors others have had aren't caused by what we thought they were caused by.
Could you tell us the rest of your system specs? What kind of video card do you have?