Files directory empty
You can find where extensions are located by looking under 

Administer>System Settings>Directories

The entry most likely has path variable such as [civicrm.files]. To find this location click on the "?" next to the following line in the info box on the top of the screen.

"You may configure these upload directories using absolute paths or path variables."

If you have installed Version 4.7 of CiviCRM the path to the extension folder is most likely: [wordpress folder]/wp-content/uploads/civicrm/ext