So i went on configuration.php and put error reporting to MAXIMUM.

And it turned out that Foundry 3.1 librairies directory was missing for Kommento according to the error message.
Strange because when i went to sleep the site was OK and Kommento was OK. The only thing i did was to install Sectionex, then i didn't check backend or frontend. Wake up this morning and there was the blank page. So it must be something strange with Sectionex, maybe the install remove Foundry 3.1, i don't know !

Problem solved for me.

Ah, SectionEx must be messing up with the Foundry folder because SectionEx wasn't updated to use the new foundry yet What you can do to fix this now is to install Komento again so that the foundry/3.1/ folder get re-instated again.

Yeah ! It's ok now : Thanks !

You are most welcome Lepinay, glad that your issues are resolved now.