Unable to login as user in my drupal 6.x website while able to access without login I am having a strange problem with my drupal website where site is working and anybody is able to surf it properly however the moment I try to login using my admin or account it shows offline message given below. What could be the reason

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Site off-line

The site is currently not available due to technical problems. Please try again later. Thank you for your understanding.

If you are the maintainer of this site, please check your database settings in the settings.php file and ensure that your hosting provider's database server is running. For more help, see the handbook, or contact your hosting provider.
As you can not login from in your site the only way to do something is from database end, if you have access to database try doing this to come out of this mess up:

Try to empty the sessions and the cache tables. Not DELETE! Empty them.
then see if you can login from http://www.yoursite.com/?q=user

Or look if your site is in maintenance mode if it is the follow instructions given here: https://www.drupal.org/node/276457

Hope above will work for you and you will get your site back to normal.
Good luck!