I have a 1.7.8.7 prestashop installed with OVH since one month. I have restore the database from the client interface of OVH, then an error 500 occur.
I restored old versions of the db but the same problem, even I have restored all of the website with old versions but the same error.
Anyone can help me ? 
j'ai modifié ('PS_MODE_DEV', true) dans config/defines.inc.php ;
alors j'ai reçu ça :
I activate the debug mode on the code so all work, from the file defines.inc.php but when I close the debug mode this new error occur: """"""""""" Warning: Zend OPcache API is restricted by "restrict_api" configuration directive """""""""""""
Your database connection not work, verify informations about database in app/config/parameters.php and verify your parameters are good