Sound in Ubuntu 10.04

[Douglas Pollard]

HI all, I had tried Ubuntu 10.10 but had no sound so I went back to10.04 
and installed Cinelerra.  My Microphone would not work so I opened 
Volume control to set it and I did something and now the sound is muted. 
Volume control shows a red X on the little speaker icon.  I don't know 
how to unmute. I tried clicking on the speaker thinking it would 
unmute.  I am in the middle of making a video and have no sound.  Any 
body know what to do about this. ??                                   
      Doug