Well,
Here goes the miracle solution, at least for me it worked. Since the Passwords in Sitebuilder are encrypted, no one can just go in and replace them.
Here's a way of putting th root password back to 'sitebuilder' .
Login to mysql.
Use sitebuilder;
UPDATE sb_users SET pswd='35cafb7a7a7ea2ff' WHERE login='root';
Hope this helps.
Best Regard's
Marco