try taking your GPU out. the intel i7 8700k has integrated graphics so plug the HDMI cable into your motherboard so it can display through your CPU. if it boots without your GPU I'm like 90% sure your GPU is dead. if it DOESNT work, your gpu is probably alive
power supply is 80plus bronze, that's average. I personally believe 600watts should be barely enough for your gpu, and also yes, be quiet is a reputable brand.