audio plays only in Windows Media Player

The audio has been working fine on my girlfriend's Windows Vista machine. But now the audio works only when you play a CD in Windows Media Player. If, for example, you go to YouTube.com and click to play a selection, nothing happens. What you see at any any selection is just a black screen, not the image.

Then I downloaded and installed WinAmp on her machine. It won't play any audio when you go to Shoutcast.

I tried to play a CD that played fine in Windows Media Player in WinAmp instead. (by changing the default player to WinAmp, from Windows Media Player) I could see the name of the CD in WinAmp, and I could also see the equalizer visual thing moving, so it appears the CD was playing in WinAmp. You just couldn't hear the sound. When I changed the default player back to Windows Media Player, the CD played and you could hear it!

As to what has changed on her machine from when the audio worked everywhere to now when it works only when playing a CD in Windows Media Player: She was subscribed to the Rhapsody music service. Instead of unsubscribing, she uninstalled the program. When her audio wouldn't work she tried to troubleshoot and may have changed settings in the Control Panel under "sound" and "Realtek audio." She may have tried other things.

Can someone please tell me how to fix this? Thanks!