Don't use any parenthesis or descriptive names like OS (C:). Just use the literal drive letters as I've been typing.
If your old music was in C:\Users\Steve Mnty\Music
and your new music is in: D:\My Music\
Then you should have:
Find: C:\Users\Steve Mnty\Music\
Replace: D:\My Music\
Please go find ONE music file on your D: drive . Find it's full path, so you can verify it. Go find that same file in your MC library. It should show the path starting with C:\Users.... . Now, run the Rename, Move, and Copy tool on that ONE file. Do the find and replace as we've discussed. BEFORE you press OK, look at the preview pane. You should see the new file name and it should match, EXACTLY, the file path of the music file you just found on your D: drive.
Does that make sense? That's what we are trying to do: Update all of the old paths so that they point to the paths on the new drive.
Brian.