I had the same thing happen to me:
My power supply?
GPU-Z reported no isses
Memtest86 reported no issues
Even ran Prime95, no issues as well
Temperatures seemed normal for my Room temperature, which is not 22ºC, maybe 27-30ºC.
It was tested in another computer, when I sent it to RMA.
Which, it came back with artifacts...
This line is having problems I EXTREMELY advice you to trade for a GTX770, what I have, sucks because I LOVE the R9 280X, but since AMD won't offer anything, I suppose we'll just make them lose money, even tho they could simply be honest and come out with some sort of list of fixes or even a new batch, but they're all just silent about, their loss.