When I first Install my Sapphire Nitro+ rx580 8gb earlier this month. I also face the same issue blank screen and PC need hard reboot.
I manage to pin point the issue to GPU cooling.
Now, I can play DMC5 at Ultra setting running at 1450Mhz. Max power draw is 201w. Max temperature 67°C. Fan Max 2900rpm.
I use TRiXX to set my GPU.
Hope u solve yours soon