Erreur 500 internal serveur error

Bonjour,
j'essaie de creer un site mais quand je copie mes fichier dans la racine (public_html)
et je donne les permission (777) j'entre au site et il me dit :
Internal Server Error

The server encountered an internal error or
misconfiguration and was unable to complete your
request.

Please contact the server administrator,
webmaster@siila.com and inform them of the time the
error occurred, and anything you might have done that
may have caused the error.

More information about this error may be available in
the server error log.

Additionally, a 404 Not Found error was encountered
while trying to use an ErrorDocument to handle the
request.

svp si quelqun a une reponse merci d'avance !