localhost web server - error 403/401

Why can´t i connect to localhost web server using any web browser???

Some times i get "HTTP 403 - forbidden access" or "HTTP 401 - Logon failed", instead.


I.I.S. (web server) is using some scripts wrote by me, but no matter what file i pick, i still get the same answers..
In my whole system i found another issue: i can´t get set the windows explorer to show hidden and system files. There must be some directive blocking the way..


(I used wmic and mmc consoles without fully understanding of what i were doing...)

And yes, the default Web Site is already configured with the rights files and folder permissions and with the propper Iternet Server API (Php5isapi.dll), though it shows "activate" button grayed out...

ups, I got W XP sp3

And don´t matter if i just write
http://localhost

alone.
It´s useless.