I'm using an HP Pavilion p624y PC with speakers built into the monitor, running Windows 7 Home Premium 64-bit. My speakers seemed just fine a second ago until I started to install World of Warcraft (WotLK). The installer window has background music that plays (and still does) and works just fine, but the audio somehow stoped playing in YouTube videos and RealPlayer downloads. Videos will play, but with no sound.
EDIT: I have no idea why, but now all Audio is working fine all of a sudden. I'm a bit confused here