I thought I was having a problem with my computer or with Adobe Flash Player as every video now comes up with the sound muted and you have to pull the volume slider across to unmute. Research on Google shows that the problem is wide-spread and there seems no solution at present - some posters think it is linked to the latest update of Flash player. Interesting that Google run YouTube but seem to be doing nothing to alleviate the problem so far. Does not seem to affect Vimeo videos or any of my other sounds or sites, just YOuTube.
John - I had just the same problem the other day - no sound from YouTube but sound from everything else. When I looked closer, I discovered that the YouTube volume slider had been set to zero - even though I'd never touched it. Pulled the slider across and - hey presto! - sound as usual... One of the joys of the internet - occasional frustration!
Will, the problem seems to have been sorted now. This morning the videos were back to normal with sound on as default.
Might even be a firefox issue... My Youtube videos like to freeze and lag behind the audio lately.
Nice to see you on here WillFly. Love your Youtube account. Seems anytime I search a tune, you have already posted a version of it.