The voice acting, sound effects and music of "World of Warcraft" help set the tone and atmosphere of adventuring in Azeroth, so when the sound doesn't work, it can really diminish your experience. Depending on what's causing your sound issues, troubleshooting options can be relatively quick or take some time and effort. In many cases, the issue can be resolved.
Reload the UI and Close Background Apps
Sometimes the issue is just a bug from an improperly loaded interface. Type "/reload" without quotes into the chat to reload your UI, which should correct the issue. Closing any apps you have running in the background can also help, as they reduce your computer's workload and enable it to run "WoW" smoother. If everything except the sound loads fine, the issue may actually be a bug in "WoW" that will be fixed with a patch or update.
Enable Sound and Music
Press the "Esc" key, then select "System" followed by "Sound" to open the sound control menu. Check the "Enable Sound" box, as well as the boxes for other sound effects you want playing, and make sure that the master volume and other specific sound sliders aren't set to "0-percent" or "Low." If the sound suddenly drops out during play, press "Ctrl-S" and "Ctrl-M;" these are the keyboard shortcuts for enabling and disabling sound and music, and accidentally hitting them during play can result in the loss of sound.
If the sound is enabled, the connection between your computer and sound system may not be secure. Check all cables between your computer and speakers or headphones. If the connection is secure, your cable may be worn out and require replacing. Find a cable that you can verify is working using other devices, and try connecting it instead. If the sound comes back, your old cable needed replacing. Otherwise, another issue may be at fault.
Adjust Windows Volume Settings
The volume settings for Windows itself may be interfering with "WoW's" sound. Click the volume icon from the task bar, then click "Mixer." This shows the Windows master volume, plus volume controls for all open apps. If the master volume, or the volume for "WoW," are muted or turned down, then sound performance will be inhibited. Turn the sound up or unmute it if necessary to restore your sound.
If you're still experiencing issues, your sound device drivers may need to be updated. Visit the manufacturer's website for your sound card and download the latest version. Follow all instructions from the manufacturer for installing the updated drivers and restart your computer. If the problem still persists, there may be an issue with your sound card's connection to your computer, or with your speakers themselves.