What is weird and what I forgot to tell you, is that the first time I opened MusicBee a few days ago, I COULD EDIT, but since I could not find my collection of music (cf initial problem of the conversation), so I did as you told me, ie uninstall MusicBee and install the portable version. But since I did that, at least I can listen to music on MusicBee but so I have this problem of not being able to edit my tracks.
I did you first method and it still doesn't work...