Hello, I've been a very long time user of AMD CPU's all the way back to the AMD 386 40mhz and all the way to my latest build the Ryzen 5 1600 with A ASUS ROG B350 motherboard.. I've always felt inclined to support AMD because their product seemed to support their customers with Good prices and quality products. But I am starting to feel a bit unhappy when I am blocked from picking a OS I want to run and am forced to use Windows 10 instead of Windows 7 which I already own and prefer to install but can't because at the start of the install the USB keyboard and mouse stop working. I've found it's a wide spread problem not linked to the motherboards but a system that is related to AMD Ryzen systems. So if I want to use my new system I am forced to install Windows 10 which is a added 100.00 cost I was not planing on spending and have to wait until I can afford to buy it. I am not happy with this at all. I like to have a say in what OS and software I use. I hope AMD will release a software patch giving their loyal customers free choices of software they want to use. This is something I'd expect Intel or Microsoft to do (just seems like their way of messing around but oh well) and am very sad AMD has taken this path.
If you want to run Windows 7 with a Ryzen system, you will need to use a board which has Windows 7 drivers, such as the ASUS Prime X370-Pro, perform a fresh installation, and use the User Finds Way to Bypass Windows 7 and 8 Update Lock For AMD Ryzen for as long as it will work, as Microsoft softblocks Kaby Lake, Ryzen, and newer updates on Windows 7 and 8.1.
See also the Andantech article: How To Get Ryzen Working on Windows 7 x64