Mining Rig won't boot with 2 or more Video Cards DELL OPTIPLEX 390

Hello everyone!

I had a few video cards at home laying around, and i decided to start mining some crypto. I have Installed windows 10 on my machine, a Dell Optiplex 390 that I bought for really cheap, the motherboard has 1x PCI-E x16 3x PCI x1 slots.

I have Risers connected to all 4 GPUs (4x AMD RX 470), the power is not a problem because I am powering them with an external server power supply, which supports up to 1400w.
The only way I can get the machine to power on is by only plugging one video card, doesn’t matter on which PCI slot, tested them all and are working.

The monitor is connected via HDMI in one of my video cards, I also enabled Multi-Display from Dell’s BIOS, but that still doesn’t seem to work.

Thanks a lot for taking your time to read this.

Have you tried powering with less attached like only 2? They’re rated 450w each so 1400w really isn’t enough for even 3 of them with only a 50w remainder, should be 10% minimum and more on lower grades like silver or below.
(The closer the max sustained load is to the psu max rating, the greater the likelihood of system faults due to electrical instability from the capacitors lacking a sufficient charge to compensate for those times when the computer increases its electrical draw so a good 15-20% cushion is ideal)

Hmm I think thats wrong about the cards’ power usage, too high perhaps though you might give it a shot and see if it still doesn’t boot with 2. If so then check the device manager and see if installed the driver and then maybe try 3 (also take into account the electrical load of disk drives and fans and other processes etc) (I suppose you could do the opposite too and try 4, if no go then try 3. You can leave the risers and just unhook the the 12v connectors.)
If not then check the graphic settings in settings/system/display/graphic settings though I don’t know if they’ll help. There’s no more more SLI/crossfire support anymore I don’t think but I assume that wouldn’t prevent powering up.