I'm doing something wrong and I'm at the point where it's smarter to ask for advice than continue to google and come up empty.
Motherboard is an MSI B450 Pro VDH Max, CPU is a Ryzen 5 2600x with the included Wraith cooler. The CPU is oriented correctly according to the manual. Case is a Phanteks P300. Hard drive is a 500 GB Corsair MX, M.2.
Two sticks of 8GB Corsair Ram in the recommended DIMM slots. Keyboard and mouse that work on other machines, same with the monitor. I've tried DVI-D and Display Port, both on-board and the installed RX580 card.
When I boot, the CPU fan spins, a light on the mouse comes on, but the monitor goes straight to sleep mode. No POST, no beeps, no BIOS. I have a flash drive ready to install Windows 10, but can't without getting into the BIOS.
I've plugged in the motherboard and power (right next to each other), the CPU power, the CPU fan, the USB 3.0 cable, the power button, and the VGA power cable for the video card. The PSU is a Seasonic S12iii, fixed cables.
I've reseated the RAM, and I'm going to try booting with one stick installed. I'm realizing now I have not reseated the video card, and I'm going to try that as well, but I feel like I'm missing something else - the integrated video should have worked even if I have the video card seated incorrectly?
The monitor going straight to power save mode makes me think the mouse and keyboard input aren't being recognized, even though the mouse seems to be getting power. I've tried different USB ports, both 2.0 and 3.0.
Can anyone think of anything obvious I'm missing? It's been a long time since I built from scratch and I'm thinking I'm missing something basic.