You will need (ISO or DVD). This serves as your recovery environment. Even if you use evaluation media, it works for repair.
Whether you are facing the dreaded error, a "Bootmgr is missing" prompt, or an infinite loading loop, this guide will walk you through every possible method to perform a Windows Server 2012 R2 boot repair —from built-in recovery tools to advanced command-line maneuvers. windows server 2012 r2 boot repair