At some stage yesterday, when clicking Configuration Drupal 7 would revert from Overlay to /admin/config and the page was blank (Page Source too). I could get to other admin pages like /admin/config/search by typing in the URL. Just the Configuration page will not appear.
I did a clean install of D7 just now. Added all the modules I needed individually and check I could see all page. After I added the Token module the problem appeared again.