All saves in backoffice doesn't work

[infrasonic]

Running on version 1.6.0.11
Saving anything (literally everything with a save/save &stay button, even when adding products and click save) brings me to a 404 page,
 

The infrarc.com page isn’t working

infrarc.com didn’t send any data.
ERR_EMPTY_RESPONSE

on Chrome and 

The connection was reset

The connection to the server was reset while the page was loading.

    The site could be temporarily unavailable or too busy. Try again in a few moments.
    If you are unable to load any pages, check your computer's network connection.
    If your computer or network is protected by a firewall or proxy, make sure that Firefox is permitted to access the Web.

on Firefox.

 

And this when I try to upload product images.

Failed to execute 'send' on 'XMLHttpRequest': Failed to load 'My Backoffice URL'.

I've tried clearing my browser cache, as well as prestashop cache at Advanced Parameters > Performance.

My website was already up for weeks, and everything was fine back then, only today when I decided to edit some products then this problem came up. Few days back I've did the php.ini thing for editing translations, but it didn't work so I deleted the php.ini file I've created (there was never a php.ini file in my root).

The Smarty Cache of my prestashop is turned on, but I can't turn it back off as doing it needs to be done by clicking save, which as I said would bring me to the 404 page..
Using Default bootstrap version 1.0 theme, with no external modules installed.

Update : Deleted .htaccess then cleared cache, nothing happened. Website's still running, save button still not working. No new .htaccess file was created so I uploaded back the one I backed up before deleting

Edited April 25, 2016 by infrasonic (see edit history)