URGENT: IIS 8.5 re-installation gives 401 error to all the websites

Hello,

After re-installing IIS 8.5, all the websites respond:

HTTP/1.1 401 Unauthorized
Server: Microsoft-IIS/8.5
Date: Tue, 29 Nov 2016 18:03:27 GMT
Content-Length: 0

What could be the fix?

Thanks and regards,
John