wp-admin shows blank page, how to fix it?

Question

I am working with WordPress 3.5.8. Yesterday I made some changes into it to a friend. I don\'t know what happened, but after some time when I try to log in at wp-admin side and

Answer 1

In my case, I was able to see the backend, but in my front I was getting a blank page...

Nothing about debugging and disabling themes/plugins was useful...
After some research, I've realized that my index.php (located at the root directory, not the theme's one) was empty!
The only content was a message saying Silence is golden.

Using a backup I had, I could get back my original index.php and get the site working again.