I use WP Security Scan, try it, it might show you where your problem is.
It told me I had to change the file permissions to my .htaccess file and my root directory (although I can never change my root…..it always changes back) and that seems to have done the job.
Maybe just me going in with Filezilla and messing around gave the new WP install a kick in the pants to get going…….I don’t know, but it’s working now.
