no sound

Yesterday I had an error problem and I finally worked through It (6 hrs), but now that I think I have everything in working order - I open the file - I record -everything seems to be working but NO SOUND! I cannot hear a thing! Last night when I turned it off things were working half way - actually I was getting an echo when I tried to record - sounded like the internal mike was overriding my mike input - so I turned everything off - now today - no sound

What are you trying to record?
What equipment?
Which version of Audacity?
Which operating system?