When you open your site php files are downloading instead of executing follow these simple steps and you will be good to go again.
first, install libapache2-mod-php5
sudo apt-get install libapache2-mod-php5
Then enable it
sudo a2enmod php5
Restart apache
sudo service apache2 restart
Clear your cache on your browser, and re-load the page.
Your php files should start executing again and you will see your site.
