GTX 580 failing? Help!

Bought a GTX 580 off a friend, was working great for about a week. Suddenly had severe graphics issues (BSOD's in game and eventually BSOD's and artifacting even while browsing the internet.) Now I have artifacts right after power-on (before windows).

I've given it back to my friend who ran the card in his system SLI with another 580 with no issues. When he removed the other 580, and used only MY 580 however, he had issues similar to mine (though in a lesser frequency), reseating the GPU helped sometimes.

I believe I might have corrupt VRAM or the VRAM may be worn out. Is that a safe assumption? and if so, without a warranty what are my options? Can I disable all the VRAM? Can I replace it? Can I buy a VRAM pci attachment?! I paid about 150 for the 580 from my friend, and so I'd hate to have only gotten one week of good gameplay out of it.

Thanks so much guys  

BTW my system is
Asus P8p67 Rev 3.0
4GB Adata DDR3 ram
i5 3570K cpu
CX600 / HX 1000 (currently using HX1000)
Crucial M4 Msata SSD
Seagate 1TB HDD
Potentially forever lost GTX 580.