Not every PC or laptop uses the exact same audio driver or card. No problem these very easy steps will help you quickly select your audio driver in VirtualBox which will fix it instantly.

First shutdown Windows and load Virtualbox

Now go down to "Audio" and click on it.

Select your audio driver

There will only be two audio drivers at the most.

In this example the default audio driver is "Intel HD Audio" at the top.
If you have multiple audio drivers just select the one you are using.
Then you can reload your Windows VM and the audio will work now.