There is somthing wrong with my computer the sound on my Instant messanger dont work and trying to listen to music online wont work either there is no sound but when i listen to music that i had downloaded works and gaming online sounds work but anything thats on the web page have no sound like when i go to YouTube to try to watch a movie it has no sound.. help? please?

thannk you

from utube site .

Why can't I hear the audio when I'm watching a video?
To make sure that you hear sound while watching videos, please check the volume controls on your computer. Also, be sure to increase the volume on other conventional video players on your computer, such as Real Player or Windows Media. This may have an effect on your computer's master volume levels. Next, check to see if your system meets these requirements for running the Video Viewer:

* Macromedia Flash Player 7.0+ plug-in
* Windows 2000 or higher with latest updates installed
* Mac OS X 10.3 or higher
* Firefox 1.1+, IE 5.0+, or Safari 1.0+
* Broadband connection with 500+ Kbps