Problems when loading an mp4-file into Premiere Elements, no mic-sound

Hello!
I am close to giving up here now. 
I record videos in-game with audio from the game itself + that I speak into my microphone. The whole procedure works fine, I create an mp4-file. When I open that file in Win10 i see and hear everything, i.e. my speaking and the in-game audio as well as video.
BUT, when I then upload that mp4-file into premiere elements to add my own intro video and outtro video I do not have my mic audio included when I click play in premiere elements - only video and i-game audio, but not my speaking.

So, mp4-file -> all ok
in premiere elements -> no mic-sound available

Why? What can I do?