From billscott92787: Check to see if this is in your settings. Right click next to ...

Examine to seat whether this is within your settings. Right click on your desktop, sound properties, from here clic Settings. You will seat Display: If you seat your top side monitor brand in present select it click apply and ok. See if this works!

Source: http://answers.yahoo.com/question/index?qid=20081130021423AANMXQa