TL:DR Solved by underclocking memory vga -50hz
So i had this Greyscreen problem since the frist days i bought my R7 200 HIS 2GB Hypermemory.
GSOD starts with random flickering, random flashes, and then Screen suddenly turns Grey, Sometimes With black Vertical stripes. The computer didnt responds even iswitch the cable hdmi port>VGA port.
The greyscreen happens frequently and in many times it happen when i run some RAM demanding application, like video editing, chrome... and its really been a trouble since i use the computer mainly for work. It almost never happens when I play games.
The temperature is fine when the problem occurs. So i guess the problem is on the memory.
Tried udate the driver and software, and it didnt work, and just to afraid to do an BIOS update, ppl said it was unfixable or something, they said it was faulty.
Well it solved when i underclocked my memory vga -50hz. and it never happened again. i guess its really faulty products then(?).