The easiest way for you to do this would be to open Lightroom with your existing catalog. Then from the Lightroom menu select File/New Catalog and follow the prompts. When you have a new catalog running you can simply delete the old one. Lightroom hasn't done anything to the images that you have imported. And the new catalog will have nothing imported into it.
I have decided that my external HD wasn't organized enough and spent days making folders of special events and by years.
I will point out that none of this organizing in your operating system is necessary, it can be done in Lightroom as well, and you can organize in Lightroom with tools that you don't have in your operating system, tools that are more powerful than your operating system, and tools that were specifically designed for photos (which folders were not). These tools are keywords, captions and other metadata. My suggestion is that instead of moving photos and folders from one place to another to achieve organization, you instead use keywords, captions and other metadata to achieve organization.