Welcome to the forum.
Unfortunately, you have posted to the Premiere Pro Forum, and you need the Premiere Elements Forum.
I will Move your post to that very active and helpful forum. Your link, and any e-mail subscriptions will follow along nicely.
[Moved to Premiere Elements Forum]
Now that we have your post in the correct forum, I have a few questions, please:
Can you give us the full details of your Imported AV files, and especially the Audio Stream information?
What Project Setting are you using? You can go to Edit>Project Settings>General, to get that info, if needed?
What OS are you running PrE 12 on?
When you Imported the Clips, did you allow PrE to Conform the Audio completely (Very Important)? For more info, please see this Tips & Tricks article: http://forums.adobe.com/message/3892177#3892177
That you can hear other Audio in PrE is a good sign.
Good luck, and please let us know a bit more.
This is the same situation that many have found themselves in lately.
It is associated with narration being generated and killing the rest of the audio in the project.
I have tried to reproduce the problem several times without success. I did reproduce it once unexpectedly. So unexpectedly that I could not reproduce it again.
But, I have something I would like you to try since you currently have the problem to work on; whereas, I do not.
The Premiere Elements user Llamadude99 wrote in the following thread
I was trying different things and I went to tools to narration. I removed the mute audio before recording, then deleted the narration I previously did and then pressed undo, to bring it back and my audio returned on my video. Very strange but it worked. I wanted to thank you for taking the time to try to help me with this situation.I really appreciate it.
We would be interested if Llamadude99's solution will work for you as it did for her. I am assuming by comment track that you are referring to the Narration track.