The IP belongs to a known WP hacker. Block all access to it in your .htaccess file. Either add the following or edit something similar already there to the same effect.
<Limit GET POST PUT>
Allow from all
Deny from 188.8.131.52
# add more 'Deny from' lines to block more bad IPs
I've never seen a message like yours before, I'm guessing your host put it up as a load limiting and/or security measure. If so, you probably need to log in to your hosting control panel to release the lock.
While shutting down your site is an extreme measure, it may have prevented your site from actually being hacked.