I went in admin to the page cercle de lumiere

I went in admin to the page cercle de lumiere and then opened upfront, made the changes i needed on the background saved checked the front end everything was fine went back in the backend page to modify the navigation title and moving the text box of the call to action and then suddenly the site collapsed and here is the error message Internal Server Error

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

Please contact the server administrator, (removed by moderator for security purposes) 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.
please advise what to do, also when trying to move the call to action (black text Box) it does not stay where i want and additionally resize badly by itself..
thks in advance for your help