I am developing for Gsoc this year and i got up one day to use the API explorer but the page somewhat fails to load. below is a screen-shot of the display 
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What Drupal theme are you using for your Civi interface? If you try switching your Civi theme to something standard like Garland, does that change anything? – Allen Hutchison Jun 23 '16 at 22:37
I've seen this once before and it was caused by a crash when fetching the list of entities. Do you have any custom code in place that defines a new entity? Try turning on debug & backtrace and run this from the civicrm home page in your browser console:
CRM.api3('entity', 'get')
May be you have a Javascript blocker add-on in your browser? You should whitelist that site allowing Javascript and then it should show up normally.
