Picked up a completely different 7970 even cheaper than the first one.
Gave it new thermal paste/pads
Simular issue, computer boots with card, when booted in safe mode or the basic VGA driver the computer works fine No artifacts/lines I even was able to play D2 with it.
As soon as I try to install a driver it freezes the whole damn computer. Tried Current AMD driver, 16.11 and 15.11. 15.11 is the only one that wont insta crash, it loads the driver but suddenly I can't get into windows I only get "Thread stuck in driver" error bluescreen and have to go back into safe mode and uninstall the driver.
Already flashed the bios to the correct one. I've used DDU to uninstall every trace of any driver before trying any of the above ones.
The only other thing I can think of is try windows 7/8.1 and use a driver for that os, or try it in a hackintosh with an apple driver.