So the situation may have arisen where you need to have your website offline, yet you need your registered users to have access to it. This could be because of beta testing, pre-approval prior to launch, or a host of other reasons. However, you have a problem. By default Joomla does not allow registered users to access a website when it is offline. So here is how you can accomplish this.
Open your default Joomla directory via your web server file manager or ftp client.
Open the folder "includes".
Look for and open the file "application.php" in your editor.
NOTE: If you do not have a fancy web editor, don't worry. Notepad can be found on any windows computer. Although this is not a pretty solution it can be done. Make sure to use the find function in Notepad by pressing "ctrl+F". Then search for offline to find the code below.
Scroll down to line 154, it should look like this: if ($this->getCfg('offline') && $user->get('gid') < '23' ) { $file = 'offline';
Change the "23" to an "18".
Save the file and you have now allowed registered users to access your Joomla install.
Note that playing with core files may create security risks, therefore do not use this method as a long term solution. Also this file may be over written with future Joomla updates.