Could you try this workaround to reset your Drupal theme?
- Delete your theme folder (or change to another name).
- Go to Administration > Configuration > Development > Performance (http://example.com/admin/config/development/performance)
- Click the button "Clear all caches"
If you are not able to access to your administration panel, you could use drush to reset the cache:
Drupal 7 and earlier:
drush cache-clear all
Hope it helps you.