gpu issue

Guys, I just replaced my GPU's thermal paste and pads. After replacing them and running FurMark, I noticed a great difference in temperature. But after about 15 minutes, the fans went to full speed and the screen went black. I powered off the system as soon as I saw this. Then, after powering it back on, the screen stayed black and I noticed the GPU fans weren't spinning. I have an RX 570 Adrenalin Edition. am i cooked?