Re: How to Re-Install
You state in the thread that you link to above:
I had originally installed my wordpressmu under /wordpress-mu/ but then moved it to the root later.
By making that simple directory switch, you’ve basically changed your site URL structure and messed up the DB.
Read this entire WordPress Codex article, paying specific attention to the “Changing the URL directly in the database” section.
Always backup your DB before making any changes–installing new plugins, upgrading, altering code in files, altering data directly in the MySQL tables, etcetera. You never know when some seemingly trivial change might mess up your entire install.