"The audio service is not running"

Beginning about a week ago I noticed my sound was not working. There is a red "x" on the speaker icon in the lower right hand corner of the monitor. When I place the mouse over it a message displays that reads "The audio service is not running."  I right click and hit "sounds" and a message comes up saying "This computer cannot play audio because the Windows Audio Service is not enabled".  I have looked at various places and everything seems to be enabled...I don't get it.

I realize this seems like a Microsoft question that should be in another forum, but I have looked all over and nothing seems to work. The reason I'm posting here is that others have said to fix it, you should right click on the icon, click sounds, when the Sound window opens up you go to recording tab and tell it to show all disabled devices.  Other icons should pop up, and then you should enable the one named Stereo Mix.  But no icons come up when I do this. I read that Dell may not have this and have seen some other threads here about this Stereo Mix issue.  But my sound was just working not long ago...so doesn't seem like it would be that??  I really would appreciate any advice.  I have a Dell Dimension E521, Windows Vista Home Edition, sound card is SigmaTel High Definition Audio Codec.

Thanks,