When you set site maintenance to offline, you lose the link to you login form as well. To get the login form, you need to do the following:
http://www.mysite.com/q=user or http://www.mysite.com/user
Do not replace the word user with your username.
If this doesn’t work, log into you database and type the following SQL commands.
UPDATE variable SET value = 's:1:"0";' WHERE name= 'site_offline'; DELETE FROM cache WHERE cid = 'variables';
If you lost your mysql password, go to your drupal installation directory. Then navigate to sites/default. You should see a file by the name of settings.php. Open this file and look for a line which looks like the following.
Then type the following:
mysql -u username -p databasename
You will be prompted for you password. Once logged in type the SQL commands listed above.