Cannot access Administration > People page
I'm not sure 100% if my solution will solve your issue or not but give it a try

first set base url in settings.php 

$base_url = 'http://baseurl.com/Drupal/htdocs';


then check if clean urls enabled from 

/?q=admin/config/search/clean-urls


just in case try to clear Drupal cache from

/?q=admin/config/development/performance