The admin section is working fine. The problem is when a user loads the front page, it gets downloaded successfully (all resources get status 200), then somehow gets rendered ( I can see the layout and content for a few milliseconds) but then it "switches" to about:blank - a blank page.
If I put the site in maintenance mode, the "up for maintenance page" gets redirected to blank too.
The version of Drupal is the latest 7.22, I also unsuccessfully applied the "Allow Insecure Derivatives" fix.
I fixed the problem. After checking most of the solutions on Drupal docs http://drupal.org/node/158043 about "WSOD" I crossed out many options.
Still, the problem was in the custom Drupal theme, more precisely in the javascript file, which is not mentioned in the previous link. After removing a part which was used for some sort of user tracking, the page started working normally.