Go to control panel and then device manager. Then tell me what it says under the sound and audio option.
EDIT: An OS is the operating system and will usually be XP, Vista, Windows 7 etc.
Exactly. If its Windows 7, head for the Desktop (The main screen) and right-click. Look for "Personalization". A window for editing your screensaver, background and other stuff comes up. Click on "Sound" and a small window will pop up with the sounds set for your computer. Head for the option labeled "Playback" click "Speakers". Your options there should show if they are active, off, plugged, etc.