Trouble getting XFX Radeon RX460 installed in Dell T5400 Workstation

[billU]

I have worked for 2 days trying to get an XFX RX 460 GPU drivers to be recognized in a Dell Precision T5400 workstation. I upgraded the T5400 from Vista to Windows 7 64 bit.

Things I have done:

Installed GPU into the same slot as the previous GPU
Installed GPU as if it was a mining machine with riser card and PCI express slot.
Changed "Digital Signature" per forum on a Help page
Changed PATH statement to reflect location of drivers
Installed Drivers in separate AMD folder
Installed Drivers in the Program Files / AMD folder
Rebooted the machine like a million times.
Installed .NET Framework updates
Installed SP1 and other Updates
Installed using supplied DVD
Installed using downloaded file from AMD website

The Device Manager shows the yellow triangle next to the device driver.

Funny thing is, I successfully installed an XFX RX 470 externally and it worked amazing!

Has anyone else solved this problem? FYI. I am trying to get this ready for my son for XMAS morning.!  Images of the errors messages are found below.


https://drive.google.com/file/d/0B7asPyfWnIHzdmpGTHNPZVd5RmM/view?usp=sharing

https://drive.google.com/file/d/0B7asPyfWnIHzRllqNmxnRW5VUUE/view?usp=sharing

[chup]

I have worked for 2 days trying to get an XFX RX 460 GPU drivers to be recognized in a Dell Precision T5400 workstation. I upgraded the T5400 from Vista to Windows 7 64 bit.

AFAIK You can only boot mentioned machine with primary video card supporting legacy BIOS. RX4XX cards are only UEFI BIOS compatible. Workaround is having graphics card with legacy BIOS as primary one, and RX460 as secondary.