I made a backup of the file signup-tos.php which is installed in mu-plugins.
Then I modified the original file (changed TOS for Terms Of Service) and then clicked on save and reload.
That's all I did. Refreshed but the site does not works.
Since I had a backup, I uploaded the same, but the site still does not works.
Please help, since the whole blog is down. Don't know how to make it work again!
Enclosed please find the original file.