Hi,
1. Is the issue occurring only when you playback video in YouTube?
2. Are you able to listen to the audio files saved on the computer?
We really appreciate your effort to resolve the issue.
Method 1:
I would suggest you to run the Playing Audio troubleshooter and check if it helps.
a) Press Windows key + W key on your desktop.
b) Write Troubleshooting in the search box on the upper right hand corner.
c) Select the Troubleshooting option obtained after the search.
d) Select View All option from the left panel.
e) Select Playing Audio option.
f) Click on Next to perform the Playing Audio troubleshooter.
Method 2:
Uninstall the Sound card drivers and reinstall
Follow the steps to uninstall the Sound card drivers and in-built speaker drivers.
a. Press Windows Key + X and then click Device Manger.
b. Search for Sound, Video and Game Controllers and expand it.
c. Right on the soundcard driver and select uninstall.
You can logon to the computer manufacturer website and install the latest driver for the computer.
http://h10025.www1.hp.com/ewfrf/wc/softwareCategory?cc=us&lc=en&dlc=en&product=5315132
Hope it helps.
Please post back with the status of the issue and we will be happy to assist you further.