Unique Audio Issue with WMV Files

I need professional help, but especially with audio.

I have a new HP Pavilion HDX with Vista Ultimate x64. All audio works, be it HD DVD, CDs, and nearly all video and audio files.
But a few specific WMV files play video but not audio. This is true whether they’re played in WMP, Winamp, or any other player, so the player issue is eliminated. Vista’s audio meter bounces as though it can hear the sound, but it doesn’t make it to the speakers.

The same files do work on my other PCs, both XP and 32-bit Vista.

You would think it would be a Codec issue, so I installed CodecInstaller and analyzed the codecs. There is no common theme among the audio codecs that I can determine. Some files have perfect audio, and others that seem to have the same codec are silent, with great video. I also took a risk and installed the well-regarded-in-some-circles K-Lite codec pack. It made no difference either way.

But when I convert them to AVI files with a conversion program, they work fine. You’d think this would narrow it down.

The sound card has current drivers and seems to work great.

I’m just at a loss. What would cause this only for certain WMV files, but they work after being converted to AVI, and codecs don’t seem to be the issue?

Thanks for any insight you can provide.