Catalin7504,   I believe the issue you are facing is due to compatibility. When I look at the supported CPUs I am showing the ES-2697 V3, but the 2697 V4 is not listed. With it not being listed we can't be certain how the system will react as it isn't tested with that specific device.  If you previously had dual CPUs, which worked correctly, then it is likely not the board or anything else causing the issue.   Let me know if this helps.
I have a R530 running with 2 x 2698 v3 and I want to upgrade to use 2 x 2697 v4. Each CPU was verified and works just fine when installed in CPU1. When both CPU are installed, the server does not POST, no video signal. I have  latest BIOS and latest iDrac. The power supply is a 1100W.Any suggestions?Thank you! 
Dell R530 no POST with second E5-2697 v4