Hi ,
I'm from Argentina. I've also have this problem with the R9 270x. I've try everything I could and nothing was working.
I tried removing all fans from the gpu and clean it. After that it worked for about 2 weeks until the black screen appaired again and I couldn't install the drivers (same as the first time). So I've tried everything I could again and nothing worked.
Then I remember one thing that I did the first time, when I remove the fans, and before mount it again, I try to plug the gpu without fans and without the heatsink, and turn the computer on like 4 or 5 times, it didn't work either but it was after that, that suddenly the black screen disappear for those 2 weeks. So I tried that again and magically it works. I don't know if it was coincidence or what, but now is currently working.
Maybe you could try that if you have nothing else to try. And please if you do comment back so I know it's not coincidence