I told him that already, but it looks he did something wrong, because he still don’t see the boot checklist and not even see Grub after his changes… what ever he did wrong 
Not for me and many other’s and AMD has sometimes problem’s too.
Did you installed with proprietary drivers or the free driver’s after reinstall?
You know you can choose between both driver’s when you first load into live boot?
Why you switching your HDMI plug at all? This isn’t automatically change.
Maybe deactivate your iGPU in Bios if you have one.
Btw. we had recently another Nvidia user with a Blackscreen after a new install,
maybe you can find some similarities to your system: