Submitted by NanoDano on Tue, 10/16/2012 - 19:23
Manually alter the Drupal theme in MySQL using these commands.
UPDATE system SET status=1 WHERE name = 'garland';
UPDATE variable SET value='s:7:"garland"' WHERE name = 'theme_default';
NOTE: There are many cache tables in Drupal 7 that may need to be flushed.