A lack of audio on YouTube can be due to a number of causes, such as an audio device that is turned off, outdated drivers, an outdated Flash plugin, or software that interferes with the playback. Each problem requires a different approach that typically requires checking the hardware, upgrading some software and getting rid of other software.
The first thing a person should do is check to see if all wires are connected to the speakers and tower, as well as to ensure the power is on. If all devices are connected and powered properly, then a user may need to update his drivers. He must click Start, then his Device Manager, and finally Sound. Finally, he must select the Driver tab and click Update Drivers.
If this does not work, he may also try installing the latest version of Flash software. Finally, he can also update his other software. He can try different browsers to see if any of them plays audio from YouTube. For browsers that don't, he should upgrade to the latest version. He may also try disabling any plugins that he has running, such as video accelerators, which can disable certain YouTube functions. Also, he must get rid of any video downloader plugins he is using.