prime x470 motherboard

I've just bought & put together a Prime X470 motherboard along with a Ryzen 5 CPU & 32GB of Corsair Vengeance RAM (2 x 16GB) Also a new 800 watt ATX PSU. It won't boot, nothing comes up on my monitor, I've tried using the HDMI directly on the mobo & have also tried a graphics card. I've...