Question PC won't turn on after third GPU - fans are spinning, no display

[octimusprime]

Hi guys, I'm trying to assemble a PC and fail to connect 3 GPUs. I started with the following specifications first:

• Motherboard: Asus Prime B450-Plus
• CPU: AMD Athlon 3000G
• GPU: 3x GeForce RTX 3060 Ti
• PSU: Corsair HX1200
• RAM: HyperX FURY Black 8GB 3200MHz

I connected all the parts (initially without GPUs), successfully booted up the PC, made BIOS settings, set up Windows 10, etc. Once everything was set up, I started connecting the GPUs one by one. I was able to successfully connect both the first and second GPU (using risers) and everything worked fine. However, after I connected the third GPU, the PC wouldn't boot up - I don't have a display, I can't get into the BIOS, but the CPU fan and the GPU LEDs work. So I tried to start the PC again with only one GPU/ without any GPU, but that doesn't work now either.

I then got replacement parts: new motherboard (AsRock B450 Pro4), new CPU, new RAM stick and did it all again. But then the same problem: I was able to connect two GPUs successfully and the third one crippled everything again. I have no display again and I can’t go back to one GPU (or 0 or 2 GPUs) so I can't do anything.

So far I've tried resetting the CMOS, clearing the RAM slots of dust, using a different monitor + HDMI cable - all with no success. Also, 4G decoding is enabled. The only thing left is the PSU, but can the problem come from the PSU if the fans are spinning, the lights on the GPUs are working, and the PC was working fine with 2 GPUs before? I must be missing something if the problem occurred 2 times with different components ...

At this point I'm really confused and am in need of help. Would love to hear your tips!

 

[Joarvi]

Try to update the BIOS or downgrade the BIOS(That worked for me).