Sound not working with Video

I have a laptop with Vista Home Premium and an old desktop with Win XP. While attending a conference in SL, i discovered that the sound is not playing when I play videos. The sound works in voice in SL. Conference personnel helped me change settings in preferences. I downloaded a new copy of QuickTime and installed. Sound in movies and quicktime works perfectly outside of SL. The old desktop works fine but is very slow. Any suggestions greatly appreciated. HELP

Hi Professor, I don't know if this has anything to do with it, but if you read the Linden Blog,

http://blog.secondlife.com/2007/12/02/second-life-viewer-susceptible-to-quicktime-security-flaw/

it says some stuff about Quicktime. It could be that whatever parcel you were on disabled Quicktime somehow?

thanks. i was at a symposium and the sound was working for others and worked on my older desktop when i logged in and out of SL. has to be something in Vista and the new SL release or sound card. but i appreciate the suggestion.