My audio went out on my computer---help?

I got a new USB speaker for my computer (which has a very awful internal speaker.) I finally got it to work by going into the Control Panel and fiddling with the audio. Unfortunately, now, the internal audio is completely gone. The only way I can get the computer to have sound is through the speaker! :( This is not good when I have to use Audacity to record things. Now, the sound is totally muffled and sounds like I am riding in a car with the windows open when I use Audacity by having the external speaker connected.

When I go into the Control Panel…it now says, “No audio available for this computer” or something like that. So, there is nothing available for me to either check a box or uncheck a box and nothing that I can re-install (or I don’t see anything.) It just says “nothing available”.

Can you tell me how to re-install internal audio to my computer? ( I have Vista). Once again (as I do every time I ask a technical question——which unfortunately is often) I am not very computer literate…so a Step 1, Step 2 format works best.

Thanks in advance!