New M/B-CPU refuses to boot

[MR ZenWiz]

Where do I start?

I decided I wanted to upgrade my Intel i7 AsRock 97 mobo combo with a
newer, higher powered processor and more memory.

I bought an AMD Ryzen 9 5950 with an ASUS Tuf X570 Pro m/b, 32Gb of
DDR 3200 RAM and a VisionTek Radeon HD 5450 video card (because the
m/b needs a CPU with onboard graphics and the 5950 doesn;t have that
and requires a video card).

I got it to boot up into the PROM, checked the specs and told it to go
ahead and boot.

Nada - black screen.

Originally I got the grub prompt, but frankly I don't know what to do
from there.

It didn't even allow PROM access every time, just occasionally.

I tried using my Xubuntu UDB drive, but even when I got the boot
prompt, it never came back with anything on the screen.

I tried disabling the UEFI secure boot in the PROM, and now all I get
is black.  NOthing else.  It refuses to boot the SSD (which has a UEFI
partition) and it refuses to boot off the flash drive.

That was a lot of work and I'd rather not have to pay for someone to
do this if I can avoid it.

Help?

Mark
Over 40 years experience building my own PCs.