iTunes on OS 10.11.6 on i Mac 24 inch, early 2009 not opening

Shouldn't that be ~/Library/itunes ?

Anyway, it looks a bit like your file permissions are messed up. I'd reboot with the keys cmd - r into recovery mode (https://support.apple.com/en-us/HT201314), open disc-utility and run "first aid". Nothing can get lost with it, but you anyway got a backup, haven't you? ;-)

hth

david

See Empty/corrupt iTunes library after upgrade/crash - Apple Community. In particular the bullet points near the end. You likely need to option-start-iTunes to choose a library, or create a fresh one.

tt2

See Repair security permissions for iTunes for Mac - Apple Community. Alternatively restore the library database from the Previous iTunes Libraries folder. Note that opening an ITL file in Finder opens iTunes with the last library file that was accessed by iTunes, not necessarily the file that you click on. If the preference that holds the last opened data is corrupt you may get the locked disk warning.

tt2

Before going nuclear, test this (these are not certain solutions, they may or may not work. But they are not risky.):

Open your Library-Folder in Finder, open the Menu "Go to" > Library (if it's not there, press the alt-key while the menu is open or while you're opening the menu...)

Create a new folder there, name it "iTunes"...

See what happens.

If it did not help, you could try to delete iTunes's Preferences, which are (again) in the ~/Library/Preferences/ folder.

Quit iTunes.

Search for "com.apple.iTunes.plist" duplicate the files into a folder (just in case) and move the originals to the trash. Empty it.

Start iTunes again.

Does it work?

I'm sorry, I've misled you. The path should've been ~/Music. The folder normally resides in your home folder and contains iTunes folder which, in turn, encloses iTunes Media folder with all your media. If you don't see it couldn't it be that at some point in time you moved iTunes or iTunes Media folder to another drive? Do you have other drives plugged in? Are you able to locate and identify the "locked disk" mentioned in the OP?

When in Finder press the key combination Shift-Cmd-G, in the search field type " ~Library/Music", hit "Go". Do you see a folder named "iTunes"? If you do, what's in it?

When you restored from the backup, what exactly did you restore?