How 'bout you toss us a bone tell us WHAT KIND OF COMPUTER YOU HAVE, pal?
I have a pc running windows 7
What tutorial(s) are you watching where you get no sound? If your computer is showing you that it's getting sound, it means it thinks it's sending you sound, so I really don't understand how you wouldn't get any audio out of your speakers.
Also, this sounds like an issue with your computer, speakers, or web browser; yet you've posted in a forum about After Effects so I don't know how it's related.