A couple days ago, about halfway through listening to a song, the sound simply disappeared.

I fiddled with the volume, tried youtube instead of iTunes, restarted my computer, tested my sound and unplugged my speakers before plugging them back in. Nothing changed.
I don't think it's my speakers, because when I turn the knob to turn them on, they make the customary crackle and the blue light appears. I tried plugging headphones into the front of my computer and they hummed, but didn't play sound either.
I checked out this thread:
http://forums.techguy.org/windows-xp...omputer-2.html
but none of my devices have a question mark or exclamation point over them.
Under 'sound, video and game controllers' these things are listed: Audio codecs, legacy audio drivers, legacy video capture devices, media control devices, realtek AC'97 Audio, sound blaster live! 24-bit, and video codecs.
I'm not really sure what any of those are (I got the computer third hand) except I believe that the realtek is the sound card?
I have an XP, version 5.1 and I'd really like to be able to listen to music again, so any help you could provide would be helpful. Thank you!
