For Administrators and Super Administrators Only
There can be numerous reasons for taking your Joomla site off-line. You don't need to take it off-line to add new articles or change the site however.
The site can only be taken off-line by super administrators or administrators: if you fall into this category, log in to the Back End Administration section.
Click on "global configuration" and then change the "site off-line" option button from no to yes. When you want to bring the site back online simply reverse the procedure.
Within this section of the Administration compliment you can also enter the message showing whilst the site is off-line.