Site maintanence offline??? Log out already???

Don't worry.
Go to your phpMyadmin or your database and run the query below to TURN ON your Drupal site again:-

UPDATE variable SET value = 's:1:"0";' WHERE name= 'site_offline';# MySQL returned an empty result set (i.e. zero rows).

DELETE FROM cache WHERE cid = 'variables';# 1 row(s) affected.