I have a project with pictures and video mixed, the video has its own sound. I want to add back ground music. So the pictures has the music, but when it comes to the video the background music fads out and you hear the video sound and then the background music fads in again.
I only have PE4, so you might have to read between the lines a bit on PE7. To do what you wish, I'd place your "soundtrack" music on the Sountrack Audio Track (at the bottom of the Timeline). One way to set the Audio Gain of that soundtrack is to Rt-click on it and choose "Audio Gain." This lets you establish the audio level for the entire Track. (There are other ways, but this is the simple route). This *should* establish a constant audio level for that entire Track. You can Fade-in & Fade-out this Track, so that the music comes up and then fades to silence at the end. The volume of the AV's Audio should not affect this Track. Now, with Keyframes, you can adjust the sections of this music soundtrack up and down, around your video's Audio, so that they do not compete for the listener's attention, but you can still keep the music at a proper level, below the level of the video's Audio.
If this is what you have done, but the music soundtrack fades completely out, when the video's Audio comes in, I do not know what setting might have been applied. I can imagine that there might be something in one of the "easy button" solutions to doing an automatic movie, but would not even know where to tell you to look for that.
Maybe list a step-by-step description of what you have done so far. There could easily be a hidden setting someplace that is handling the audio gain automatically, which is not what you want.