Graphic Cards :: HD7970 Gives Code 43 In Device Manager / Drivers Won't Install

I recently bought a used Sapphire HD7970 GHZ Edition 3GB, which I got quite cheaply but it did need a little work doing to it.

Firstly the fan cable had, in the hands of the original user, somehow snapped and they had repaired it to run on a normal motherboard 4 pin fan lead. When I got the card the DIY repair had practically fallen apart but I was able to reconnect it all and both fans do spin (not sure if they are running fast enough but they are spinning and moving a little bit of air).

Anyway, second problem was the card had one of the two BIOSes flashed with an incorrect BIOS (seller said it was a BIOS of a different model of 7970) and needs reflashing.

So I fixed the fan lead, verified at least some cooling was happening and was able to get to Windows (8.1 64 bit) with it. However, in the device manager the card has the yellow exclamation mark and says "Windows has stopped this device because it has reported problems. (Code 43)". I tried installing the AMD drivers regardless but they fail with warnings though still prompt to reboot, I rebooted on the hope they might have still installed but next thing Windows blue screens (well the Windows 8 version of it) with an unhandled exception warning and does this every time until I make it do a system restore then the card operates like it did before in that it outputs a picture but won't take the driver and fails to run anything more than 2D applications.

The seller has confirmed the good BIOS is already selected (he said it won't even boot to Windows on the other one) and recommended some beta drivers but these didn't work. I have also tried using Display Driver Uninstaller to remove all traces of old drivers (and manually deleted all AMD/ATI files and registry references) but no progress.

So why am I getting the code 43? Is there a diagnostic program that can tell me exactly what is stopping the card from working? How I might get this card up and running again?