Yes but no. When I deactivated the plugin, the site went back online. Not working now since I added the script. If I remove it (I will do this now, I only let everything that way so that someone didn’t just walk through and say that the site is ok), everything will be back to normal.
So how do I add the script (plugin or not) and keep my site working please?
If Piwik PRO WordPress plugin in some reasons is not working properly with your site, you can add script manually using a theme editor from the Administration Screens > Appearance > Editor menu in WordPress Admin, according to this instruction: Install a container (with a tracking code) • Piwik PRO help center
or use other editing files method described in: Editing Files | WordPress.org