I have Microsoft Windows XP.
I tried to check if the audio volume is on mute however, it tells me that I have no audio device.
And for the last one does iTunes count. I tried using that and the songs didn't play either. They were both working fine until yesterday.

I just thought of something. My sister tried to play a DVD on my computer because we have somwething called CyberLink PowerDVD. The sound didn't work on that either. Do you think that that had somehting to do with it?