Oops! Something went terribly wrong with your theme and you can't get into the admin. Have no fear.... you can get back to a Drupal default theme setting it in the databse. Just run a few commands and you're back to using Garland!
UPDATE system SET status=1 WHERE name = 'garland';
UPDATE variable SET value='s:7:"garland"' WHERE name = 'theme_default'; TRUNCATE cache; TRUNCATE cache_bootstrap; TRUNCATE cache_block;