Cant get the site out of maintence mode
If your description of what you do is accurate, the problem is simple to solve.

Clicking "Go online" is only the first step required to take your site out of maintenance mode.  You also need to remove the tick from the box to the left of "Put site into maintenance mode", and then click "Save configuration".

However, if you go through all these steps, and it still fails, you need to update your question to accurately descibe what you do, and we'll take it from there.