If the video plays but you don't hear any sound on Youtube then possibly there is an issue with your browser. To fix no sound on Youtube you need to check these settings -
1. Check your Volume is Not Turned Off
2. Use Another Web browser
3. Try an incognito Windows
4. Make Sure you Haven't muted the video
5. Use an Audio troubleshooter
6. Increase Volume in Volume Mixer
See also - https://onlinegeeks.net/youtube-not-working-how-to-fix/