Wordpress site showing 500 internal server error after wordpress automatic upgrade

Please note: I do not use cpanel. Experience of virtualdmin is needed to take on this project. Ftp also available. Hi. Guys.. This site was working with no fault. It is a wordpress site that has been fully customized. But after I received an email from wordpress of an upgrade my site was showing 500 internal server error message below. I jus need you to restore it back. Thanks #### Internal Server Error The server encountered an internal error or misconfiguration and was unable to complete your request. Please contact the server administrator, root@localhost 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. ####