Enabling sound

[Jean Hollis Weber]

I'm feeling totally stupid right now, because I have been unable
to get sound working, either through the computer's speakers or 
through a headset. (Both work fine under Windows.) The volume 
control is not muted, and it's set to a reasonable level. Is 
there some other control I need to change?

And while we're on the subject of sound, how do I test whether 
the microphone input is working? I don't want to record from the 
mic, I just want it for using with services like Skype. I have a
headset that plugs into the mic and speaker sockets on my Dell
Inspiron 510m laptop. I have been unable to get the mic working
under Windows, although the sound-out (through the earphones or
through the computer's speakers) works fine... so I'm not sure if 
there is a problem with the mic-in socket or what. Maybe I need a 
USB headset?

Any suggestions?

Cheers, Jean