I had the same problem with my R9 280x graphics card - the monitor started to get faint flickering horizontal lines and then the screen would go black for a few seconds and come back. It would do this repeatedly for a while (up to 10 minutes, then it sorted itself out and was just fine for days. Strangest thing was that it only happened periodically.
We worked out that it happened when my wife was in another room using one of those machines that you stand on and they shake/vibrate. There must be some interference from the shaking machine that affects the graphics card. Sounds weird, but that was the ONLY time the card played up, and my second computer, using an old Nvidia GTX670 card had no problem. Since I run both computers through the SAME monitor, it definitively shows that only the AMD was being affected by the interference.
Seeing a few of these posts around, it seems that the AMD 200 series might be particularly susceptible to interference - Phones, radios, shaking Gym machines.... If you are having problems where the screen goes black for a few seconds, then comes back, goes black again and comes back etc, try looking for causes of interference and turning them off.