You will notice that recent released version of WordPress requires PHP version 5 to run on your site. Some web hostings are still using PHP 4 while many web hosting offers both PHP 4 and PHP 5 in their shared hosting packages that they allow you to switch between PHP 4 and PHP 5 with their hosting administration. If you can’t find this option, you can enable by using two lines of code in .htaccess file.
AddHandler x-httpd-php5 .php AddHandler x-httpd-php .php4
If you already have .htaccess file, add those lines which I mentioned above. I hope this helps!