I installed concrete5.5.2.1. Everything seemed to install OK, but when I clicked to enter the next phase as admin, it said;
It shows top header with concrete image at top left.

Page Not Found
No page could be found at this address.

I have it installed in the root directory (not sub). I looked at index.php and saw a required. I tried setting absolute path but it did no good. I made .htaccess with

RewriteEngine on
RewriteCond %{REQUEST_FILENAME} !-f
RewriteCond %{REQUEST_FILENAME} !-d
RewriteRule ^(.*)$ /index.php/$1 [L]

still nothing

Any help will be appreciated