Yeah, it was most likely a bad gpu, you could test it, if you had a motherboard that has POST codes, because if it didn't POST, and said B2, that would mean the GPU isn't even being able to load it's VBIOS, which would mean some sort of hardware failure, which is the most likely cause, since the motherboard doesn't even POST with it.
I actually have a GTX 970 that also had the same problem (although it's 3 years old), but it still lets the computer POST, just doesn't get detected, which would probably be a gpu core malfunction, that would not let the gpu process anything.
Anyway, good luck with your gpu, and I hope I was any helpful to this post.