I recently built a new PC with a B650-E WiFi motherboard, a 7800X3D processor, 32GB of RAM running at 5600MHz, a 500GB M.2 NVMe SSD, and a 750W power supply. However, when I try to power it on, it turns off right away. I know the GPU, power supply, and SSD are functioning well, but I don't have a way to test the RAM, CPU, or motherboard. I've tried different RAM, updated the motherboard BIOS, and even unplugged the GPU to see if the power supply is insufficient. What steps should I take next to diagnose this issue?
5 Answers
Make sure all your front panel cables are connected properly. I once had the power switch connected to the LED header, resulting in the same issue—power on for a moment and then off. It's worth double-checking your setup.
If you can’t get into the BIOS, try bench testing the motherboard outside the case with just the power supply and CPU connected. If it doesn’t power on with just those, you might be looking at needing a new motherboard or CPU. You can also take them to a repair shop for testing.
It's a long shot, but if your motherboard has a small mirrored chip, sometimes these can overheat if they don't have proper cooling. Check to see if that chip is exposed and not covered by a heatsink. Also, ensure your power supply is good quality.
What power supply are you using? How do you know it’s functioning correctly? Try booting without the GPU, SSD, and just one stick of RAM. This could help isolate the problem to a specific component.
Double-check your cooler installation. Sometimes, if the cooler isn't installed correctly, the CPU can overheat almost immediately, causing the system to shut down to protect itself. You mentioned the PC doesn't even make it a second into boot, so that could be a factor.

Thanks for the tip! I don't think it's overheating since it barely powers on, but I’ll check the cooler installation just in case.