New PC Powers On but Shows No Display After Restart

I just finished building a new PC. On the first boot, it powered on and displayed the BIOS, but I couldn't get it to boot from my USB installer to install Windows. After restarting several times, I shut it down and stepped away. When I returned, the fans, lights, and GPU powered on, but there was no display. I tried clearing the CMOS with the button on the motherboard's rear I/O panel, and now the motherboard shows a yellow diagnostic light. I've tried connecting the monitor to both the GPU and motherboard, reseating the RAM, and removing the GPU, but still get no image. What should I check next?