Go into your computer's Control Panel. You can access this by clicking on the start icon at the bottom-left portion of your screen. You will then see an option for getting into your Control Panel.
Click on the Hardware and Sound tab to access the audio controls of your computer. This tab will give you the opportunity to customize settings within your computer's built-in audio card.
Click on the Sound tab. This will pull up the available audio resources for your computer's audio output. You will see one checked for enabling, and usually others that are lying dormant.
Disable the sound card by clicking "Disable" from the multiple choices on that screen. This will turn off any sound that is being sent to the speakers of your computer. The background music that once played while you browsed the Internet will now disappear, at least until you enable the computer's sound card once again.