Dell Vostro Sound Problem

I have Windows XP on my Dell Vostro 1500, and SigmaTel Speakers built in. I could play sound on my media player, but when I try to play any kind of sound on the internet, I can't hear anything. I've tried to fix the problem by looking at settings, but no luck. I would have to call Dell I guess if there is no answers here. Any way to fix this problem?

 

Help!

 

check drivers, and or try re installing your web browser i personly never had a problem with Firefox

 

or OS