i bought a old computer today as a "first computer" for my little boy, and I can't figure out what's going on with the sound - the monitor is a viewsonic 17ga perfect sound with built in speakers. The computer is a HP running windows xp. i checked all the volume controls and fixed the settings, but nothing. the speakers on the monitor are on (humming) but not registering anything. no luck with headphones either... any advice?