I've clicked on the "Listen to the archived event audio" link and instead of seeing an embedded media player, I was offered to open the following link in the Media Player:
It appeared to be a Windows Media stream that played just fine in my standalone Windows Media Player.

I don't really know what to suggest. Take a look at the volume and the Mute button.

You can also try to record the Windows Media stream with a streaming media recorder like freeware GetASFStream. See whether WMA file will play fine from your hard disk.