I just upgraded Ubuntu and unfortunately the MediaWiki installation broke. There was no debugging output on the screen (for obvious security reasons). So, I just had a blank page on the screen.
The first thing that I did was show the debugging output but editing the LocalSetting.php to enabling
$wgShowExceptionDetails = true;
After refreshing the page, the error appeared as
/var/www/includes/db/Database.php: DatabaseBase::factory no viable database extension found for type 'mysql'
It turns out the problem was php not connecting to MySQL properly.
sudo php5enmod mysql sudo service apache2 restart