Running Setup:
http://yoursite.com/setup
Also, I assume you meant you meant these:
/www/all-folders-here-except-core/config.inc.php
/www/all-folders-here-except-core/config.core.php
/www/all-folders-here-except-core/connectors/config.inc.php
/www/all-folders-here-except-core/connectors/config.core.php
/www/all-folders-here-except-core/manager/config.inc.php
/www/all-folders-here-except-core/manager/config.core.php
Make sure the core path is correct and ends with a slash in all three.
Yes and still the same problem: after the step "Install Options", choosing option "Upgrade Existing Install", then "Error 503" : Site temporarily unavailable.
I wish I had an answer for you. I don't know what might cause that.
Try watching the network tab in dev. tools in Chrome or FF (Ctrl-shift-i) as you run setup.
You might also go into the DB and look at site_status record in the modx_system_settings table. It should be set to 1.
It might also be worth checking that you don't have any php.ini files causing incompatibilities with MODX. Or that you don't need any php.ini files to make your environment compatible. Time zone being set wrong by the hosting company can be a problem.
Could there be an old .htaccess file present from a previous installation that is causing a problem?