Ok, still the same problem, just now installed new fresh clean version of php 3.0.6 without any MOD or theme, and automod did it's part, everything is in place where it should be, after that i entered in my url http://www.mydomain.com/phpBB/install_seplogin.php
and it forwarded me to my board index, so I went back in admin index and tried to change my login name and as soon as I clicked save, screen with success went on and when I clicked anything to move from that screen, it automatically logged me out as user and forwarded me to my board index again, so I tried to login again and it popped the screen i quoted in my 1st post.
And that's all, so i don't know did I install the install_seplogin.php with putting it in url or not, but it seems it's not installed. I have no idea what it's sopose to tell me for me to know if it's installed or not.
Hope that helps.
EDIT: I figured it out
I have been keeping the install folder and trying to install it without deleting it, how stupid
Anyway thank you so very much for your time and effort, it's priceless.
Thank you once again, working like charm.