Quote from: Agozyen on December 30, 2017, 01:27:24 PM

Quote from: elissa on December 30, 2017, 11:36:36 AM

Quote from: leonix007 on December 29, 2017, 03:09:33 PM

Quote from: elissa on December 29, 2017, 12:51:00 PM

I have an update. I've disabled the intel virtualization technology and hd audio. I've changed the top of lower usable Dram from dynamic to 1gb, and PCIE link speed from auto to gen3 for all pcie.
After that I have managed to connect 3 graphics cards.

However, when I put the 4th one (the last graphics card I have) the computer doesn't switch on. I have just a black screen and a b2 code on the motherboard. How can I solve this?

Make sure you have enough PSU power rating watts to supply your 4 GPU's, What are your GPU types? check also the 4th GPU if its connected correctly thru powered riser and your PSU.

much better if you could tell us your PSU power rating and your GPU types

I doubt it is the PSU. I have a SeaSonic - PRIME Gold 1200W 80+ Gold Certified. My graphics cards are Radeon Pro Duo Professional with 32 GB memory. Their consumption is 200 w maximum while mining.
There isn't a power supply issue. I guess it is smth related to the motherboard.
It is not even starting. The monitor just turns black and there is the b2 code on the motherboard.

You cannot eliminate your PSU as the culprit. Do you have a power supply tester by any chance? Have you tried switching the power supply connections to the individual cards? Troubleshooting is a game of elimination a lot of the time. You have not proven that your PSU is not the problem. Having said that, check your USB risers and try switching them around. Is your monitor connected to one of the cards or the motherboard video?

Agozyen is right you will not terminate the possibility that the PSU might be the problem just because of your calculations for a single GPU, it is really a process of elimination. I might be your motherboard, the GPU, storage, ram, wiring, PCIE raisers or even the CPU. If you have a different parts to swap in your rig you can do that to pinpoint the problem and it will be much easier but I doubt you have extras. I will be time consuming but I hope that you will find what is the problem on your rig.

P.S
Try to exchange your PSU to a 1600w if you can might be that the cards are pulling more wattage from your socket.