No sound

Hello,
I have a Dell desktop with win xp. I had sound via headphones, and suddenly it was gone. When I go into "sound and audio properties", it says that there is "no audio device". When I try a test sound, it says "windows cannot play the sound...sound card may be in use". When I go to task manager, it doesn't show any other program running. Also, I had tried before the sound went out, to put a volume icon on the task bar. It said that I couldn't do that as I didn't have the program for it (I only had sound via headphones). Now when I go to that page, I cannot even choose the icon option, as it says "No audio device", and the whole page is greyed.

I have gone through the troubleshooting guide exhaustively with no avail.
Any ideas?