Websites wont work after upgrading to PHP 7.1

Some of my websites won`t now work after up-grading to PHP 7.1, on my VPS, so i have down-graded back to PHP 5.5 using "yum install ea-php55" to get them to work again, but to no avail, even re-building the server they wont work, and up-loading fresh back-ups of my websites, and still wont work, i can`t get any error logs either, i can`t understand why. Can anyone help ?