Dashboard and index page viewing as ‘plain html’

Hi, my blog is located here https://www.rsg-online.com/blog .. it gets redirection from https://www.rsg-online.com. My main folders are placed at /blog . This problem started yesterday out of sudden, I’m not sure if my servers got hacked or anything but it certainly got me worried, everything was working perfectly before.

The former version is 2.1.3 when this problem happened. I updgraded it to 2.2 through Fantastico control panel but the problem still the remain the same. I already disabled all plugins and even switched the theme to the defaut wordpress one, but it’s still not viewing properly.

There’s another thing I noticed, my Login link from the index.php is linking to https://www.rsg-online.com/wp-login.php instead of https://www.rsg-online.com/blog/wp-login.php.

All this happened suddenly, im not sure what triggered this error.

Your help will be greatly appreciated.