Axon

That happens to me a lot, I sometimes open CoD4 and no sound at all, I use a Soundblaster X-Fi XtremeGamer, my problem was that I was having TeamSpeak running in the background, I disabled it and I had my sound back, then I just ALT+TAB out of CoD4 and started TS, then I'd still have sound.

It's annoying, but better than nothing

If that doesn't work:

- What sound card (if not onboard) are you using?
- Did you install the correct drivers?
- Are you sure, if you have a sound card, you disabled Onboard in BIOS?