Yes - that's OK - I'm hoping the items you've hidden will not appear this time - if so and you're certain they are not needed you can go through the folders and delete them. The reason you cannot mouse delete in WMP is the complex library structure in W7
- you have the 'explorer' Music folder AND the 'My Music' folder which contains the original file. Items deleted from the explorer library still show up in WMP but cannot be deleted. So it messes up the library.
I'll advise on how to delete the hidden stuff if the WMP library is looking better.