CPU: Intel(R) Core(TM) i3-2120 CPU @ 3.30GHz
MOBO: Manufacturer: ASUSTeK COMPUTER INC.
Product Name: P8H61-M LX3 PLUS R2.0
This is weird but the only OS I've found this machine doesn't work with is Windows 2019 Server. I have no idea, when 2008, 2012 work fine. Windows 2019 also works with the same software (KVM version) on a different MOBO and CPU, so I suspect it is something CPU or MOBO related that is not playing nicely.
Windows 2016+ (eg 2019) will NOT boot without using the "-cpu host" parameter which passes through the host CPU.
On most machines I run, especially server hardware this doesn't seem to matter (eg. I normally just use the default QEMU-CPU and all is fine even on 2019 and 2016).
When booting my Windows 2019 template all I get is the Windows logo: