Error 500 (Internal Server Error) After Clearing Cache
Somehow your site has entered a broken state since the Views module depends on ctools but it's not enabled.

What you need to do to fix it is to:


Enable the ctools module in the database, by running the following SQL UPDATE system SET status = 1 WHERE name = 'ctools';
Truncate all the cache tables in your database.
(Might not be needed) run $ drush rr, requires drush and the registry rebuild extension.
Run $ drush cc all requires drush.


Going through the above list should fix your site. Messing with your sites cache table can be a bit dangerous if you don't know what you are doing since drupal caches what modules it needs to load for performance.

You can read more about and download drush and registry rebuild on drupal.org.