How to restore sound playback when viewing internet videos?
This is a problem that can occur in Internet Explorer after an update.
First, check that sound can be played back from, for example, a sample track in Windows Media Player. Ensure you have working speakers or headphones plugged in, and that your system sound is not muted.
Next, in Internet Explorer go to the Tools -> Internet Options -> Advanced panel. Scroll down the list to the Multimedia heading.
Now make sure the box labelled "Play sounds in webpages" has a tick in it.
Lastly, click OK
Try playing e.g. a YouTube clip in the web browser. You may need to quit and restart your browser if sound is still not being played.