[Homebuilt] CPU fan spins once then stops. No post

Hello.

I've assembled a new system, but I'm having trouble getting it to power on.

CPU: AMD A4-3400
MB: GIGABYTE GA-A75M-UD2H
PS: CORSAIR CX430 V2
RAM: Patriot Signature 8GB (2 x 4GB) PSD38G1600KH

This isn't my first build, but I'm running out of ideas. When I press the power button, the power LED flashes briefly and the CPU fan starts to spin up, then nothing. Pressing the power button again does nothing until I flip the hard switch on the back of the PS, wait a moment, then turn the switch back on.

I've verified that the power supply is properly connected (24 pin + 4 pin). I checked the CPU and heat sink seating. I tried one stick of RAM in various slots. I reset the motherboard and checked for unneeded risers which could cause a short. I disconnected all the front panel connectors and tried starting the system with just the PS button attached. I tried starting the system by shorting the front panel power button wires. I cleared the CMOS. I tried with a different power supply (old Ultra 550W modular). In that case, the CPU fan would weakly spin for a little bit, then stop, and the cycle would repeat. This is causing me to suspect there is a power issue somewhere.

After work I'm going to try removing the motherboard from the case and starting it either outside the case or in a new one. Sadly, the HTPC case I bought didn't come with a speaker, so I couldn't listen for potential error codes. I'll take one out of a system for testing after work. One concern I have is that Gigabyte's website states that the A4-3400 is supported since BIOS F2, but that the A4-3300 is supported since F4, which is fairly recent. The two chips were released on the same date, and I'm wondering if Gigabyte has a mistake on the website and I need to flash the board. Being a new platform, I don't know anyone with another FM1 board or CPU.