Doug, go to start - settings - control panel - sound

There, check the recording setting, looks like you've got the "what u hear" option selected. Depending on where you've hooked up your guitar, you need to activate the line-in or microphone setting. It may also no be called that, depending on your sound card, mine says "stereo mix".

Happens to me all the time when I go in chat rooms, those things mess up with your settings, sometimes muting the line-in.