Hello, new here.
Anyways, I had the same problem here as well. WMP just kept updating my library all the time and it took about 80% to 100% of my CPU. However, that stopped today on my Windows 7 because I figured out how to stop it from doing that without jeopardizing my music files.
If you open up WMP, and if you go to where the libraries are at, just right click on on the library you want (like the Music Library) that's on the left hand side, or simply click on Organize -> Manage Libraries -> Music (or any other), and right click on all the folders that are listed and choose Remove. It will just remove the folder from WMP Library and not your computer.
You should also do the whole thing with the options and removing the internet stuff (might be better).
Anyways, it worked for me and now it will never update any folder unless I choose the folder. WMP doesn't take up that bunch of CPU anymore.
I hope this helped someone