AMD tech support can lend some a processor to get around a problem, aka a “Boot Kit”. They have recently updated this procedure:
Unable to Boot New Desktop System Configured with AMD 2nd Generation Ryzen™ Desktop Processor, and AMD Socket AM4 Motherboard
Article Number: PA-100
This document provides information on how to resolve a specific boot issue that may be experienced with some 2nd Generation Ryzen Desktop Processors when installed on an AMD Socket AM4 motherboard.[…]
https://support.amd.com/en-us/kb-articles/Pages/2Gen-Ryzen-AM4-System-Bootup.aspx
