My guess off hand would be the PSU...take a look at what it pulls on the 12v rail....wouldn't want to go much less than ~65A on a 12v rail. Installing reinstalling the drivers is fine but isn't the problem, most likely. It also could be you have simply landed a defective 380x card, in which case check with your reseller ASAP. I'd bet on one of the two.
My PSU output
Output Current +3.3V - 25 A
+12V1 - 30 A
+12V2 - 30 A
+5V - 25 A
-12V - 0.5 A
+5VSB - 2.5 A
I have been scouring the net now for a PSU that gets at least 65A on the 12V rail.
And it seems I would need at least a 800Watt supply that would cost about the same as my new GPU.
Seems incredibly outrageus,
So I got a new PSU for christmas, which should be sufficient. A CX750M from Corsair.
Error still there. This is the second R9 380x, and I had the other one swapped.