fixed it at last
a blatent cut and paste job
http://wizkid.wordpress.com/2006/09/15/no-audio-on-youtube/
"Yes, I like everyone else out there have been having way too much fun on youtube. Now I have a Windows XP Pro 64 system. I use Firefox and on occasion (when I have to) IE 6. So I’m not sure when it happened, but one day I noticed audio wasn’t playing on YouTube videos.
The first thing I did was follow the Youtube “help” suggestions. I checked all my media applications. Check. Checked my system audio. Check. Checked across different browsers. Check. Still no audio. Just on Youtube.
I needed my Youtube fix! So I set out on my own, uninstalling and reinstalling Flash player (which Youtube requires). No go. Upgraded Windows Media Player. No go. I clicked on all kinds of stuff. I tried codecs, xvid, etc. nothing.
Cut to the chase this is what to do (or at least what I did): Went to this site:
www.Free-codecs.com and downloaded K-Lite Codec Pack. Install this nifty little app. Then browse through your start menu: Start - Programs - K-Lite Codec Pack - Configuration -Codec Tweak Tool
From there click the button for: Fix non-working system sound
And that’s it! Don’t know what happened, or how it happened. And I’m sure this is a great little app that can do way more than what I used it for. So if you run in to this problem, try this fix for it.."