No more log-in

Hi there,
when I try logging into my wordpress installation with https://www.marcobutz.de/wp-admin there is the following error:

Internal Server Error

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

Please contact the server administrator, [email protected] 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.

Can you clarify? What to do?
Regards
Marco