Sapphire HD 4870 Artifacts, anything I can do to fix it?

Hi all,
So I bought a used HD 4870 off eBay for £16 (bargain) because the seller couldn't test the card so I didn't know whether it would work or not. I took the risk of buying it to see if it would work or not as I would like to upgrade the GPU in my secondary computer.

Here is what I've found. When booting up, the screen has white grids and lines and other artifacts when in the BIOS menu and the "Loading Operating System" screen (I have a Gigabyte GA-990FXA-UD3 motherboard) but then when the system gets to the OS boot screen and further, my screen just flashes on and off, constantly "going into sleep mode". So I can't see anything to do with Windows on the screen.
I had a Sapphire HD 6870 Flex edition graphics card in my system previously, and I hadn't changed any drivers or anything, but I doubt that's got anything to do with the problem as there are artifacts before the system actually gets to the OS.

If I disconnect the 2 x PCIe power connectors to the graphics card, the system flashes and beeps a red message saying that the power connectors aren't connected, but there are no artifacts on this flashing message, the artifacts only appear when both power connectors are plugged in and in the BIOS screen / boot. My PSU is a Corsair TX650v2 if that helps.

So really my question is whether I can do anything to save this bargain graphics card and possibly squeeze some usage out of it. I have considered the whole "baking" option as I know that has worked for some people, not sure whether to try it yet though. I have already taken the heat sync off and cleaned it, and cleaned and applied some Arctic Silver 5 thermal paste, didn't help with the problem at all.

So yeah, any help would be much appreciated!