Problem Downgrading Windows 8.1 To Windows 7 On Hp 19-211w Aio Desktop.

Hello Everyone!
I am having a problem downgrading a clients machine from Windows 8.1 64 bit to Windows 7. It boots off the Windows 7 CD, and gets to the Windows is loading files screen. The progress bar fills up and it switches to the Windows 7 splash screen for a few seconds and then it blue screens with this message, 'the BIOS in this system is not fully ACHI compliant. Please contact your system vendor for and updated BIOS. 0x000000A5.
I have flashed it to the latest BIOS and it has no effect. I have reset the UEFI settings within Windows and disabled UEFI in BIOS while enabling legacy boot. I have done this on several other HP machines for clients and when rebooting after the UEFI reset, just before the HP splash screen I would get a message telling me to enter the 4 digit code and press enter to complete the reset. On this machine, I do not get the code to reset it.
After some googling I found mention of it there being problems boot from the Windows 7 CD. So I prepared a Windows 7 boot flash drive with Rufus and a Windows 7 iso. I change the BIOS setting to boot from the flash drive and I get to the exact same point in the install before it blue screens again.
Has anyone else run into anything like this? I have never had an issue downgrading like this before. Any ideas, suggestions, input, or opinions will be greatly appreciated. Thank you all in advance!
Respectfully,
George D.