Recently bought a used Mid 2011 iMac. Passed all hardware tests no problem. Reformatted and did a fresh install of Capitan upon purchasing. Been working great for 2 weeks and then it randomly shut down to a white screen with vertical black lines, see image. I've been googling and really don't see anything about this issue. It's got a Samsung 850 EVO SSD I'm running SSD fan control on SMART mode. Rest of the specs are in the screenshot below. Any help would be greatly appreciated! thanks!