Desktop Boot and Lockup

My client purchased a new HP Envy desktop to replace the aging desktop she has now.

The plan going into the service was to take her SATA SSD (Windows 10 installation) she had in her old desktop, connect it internally to the new Envy desktop (also Windows 10), boot into Windows, all is copacetic. Well, as they say, nothing ever goes according to plan.

Discovered her SATA SSD was MBR, and this particular Envy is GPT/UEFI only. No problem, back up her original Windows 10 installation, format her SATA SSD, convert the SSD to GPT, restore her installation, try to boot again. Unfortunately, this was the first instance of seeing "inaccessible boot device". 

Just to be certain, I brought her SATA SSD home with me to my personal computer. I made sure the boot files were restored and made sure that boot mode in my BIOS was set to UEFI. I was able to boot her SATA SSD successfully with my system. Perfect...so why isn't her SATA SSD booting on her new Envy?

I tried something for curiosity's sake. I have a SATA to USB 3.0 adapter. Very convenient piece of gear. I tried booting the SATA SSD with the USB adapter connected to the Envy. Curiously enough, it worked. I was blown away. So we can confirm that the HP Envy can boot the SATA SSD, but only through external means. So bizarre.

I went ahead and checked to see if her old desktop was capable of booting UEFI. Sure enough, it was able to boot. My client thankfully has a desktop she can use, but all of this troubleshooting leaves me stumped.

So in summary, GPT/UEFI SATA SSD behaves thusly:

• Can boot via UEFI on my personal system (motherboard is MSI B550 Gaming Pro with up-to-date BIOS).
• Can boot via UEFI through SATA to USB 3.0 adapter connected to new HP Envy desktop.
• Can boot via UEFI through the client's old desktop (Intel Ivy Bridge or Haswell-based, I know it's an i7 processor in a socket 1155, MSI H61 chipset motherboard). 
• Can NOT boot via UEFI through an internal SATA connection in the new HP Envy desktop.

Is there something I'm missing here? Will secure boot or TPM prevent me from booting from the SATA SSD?

My next experiment would be to try cloning the SATA SSD over to the included NVM-E SSD in the HP Envy. I fear that I would: a) lose the brand new, fresh install of Windows 10, b) still not be able to boot with the old Windows 10 installation. I believe something in the motherboard hardware is preventing me from booting any Windows installation that did not come included with the new Envy desktop.

Has anyone encountered a situation like this? Any assistance would be great. Thanks in advance!

- Aaron